Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.55   13.251%   $248.6426   $248.64   $248.65   $248.60  
  Purchase #2 $205.58   9.537%   $225.1862   $225.19   $225.20   $225.20  
  Purchase #3 $244.39   3.156%   $252.1029   $252.10   $252.10   $252.10  
  Purchase #4 $125.65   10.339%   $138.641   $138.64   $138.65   $138.60  
  Purchase #5 $223.64   4.475%   $233.6479   $233.65   $233.65   $233.60  
  Purchase #6 $247.51   8.686%   $269.0087   $269.01   $269.00   $269.00  
  Purchase #7 $239.85   4.392%   $250.3842   $250.38   $250.40   $250.40  
  7 purchase totals = $1,506.17       $1,617.6135   $1,617.61   $1,617.65   $1,617.50