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 $114.25   5.617%   $120.6674   $120.67   $120.65   $120.70  
  Purchase #2 $165.57   5.561%   $174.7773   $174.78   $174.80   $174.80  
  Purchase #3 $174.73   7.209%   $187.3263   $187.33   $187.35   $187.30  
  Purchase #4 $78.66   4.471%   $82.1769   $82.18   $82.20   $82.20  
  Purchase #5 $167.77   3.506%   $173.652   $173.65   $173.65   $173.70  
  Purchase #6 $181.31   9.497%   $198.529   $198.53   $198.55   $198.50  
  Purchase #7 $43.58   6.156%   $46.2628   $46.26   $46.25   $46.30  
  7 purchase totals = $925.87       $983.3917   $983.40   $983.45   $983.50