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 $221.75   11.840%   $248.0052   $248.01   $248.00   $248.00  
  Purchase #2 $170.70   7.827%   $184.0607   $184.06   $184.05   $184.10  
  Purchase #3 $65.58   13.830%   $74.6497   $74.65   $74.65   $74.60  
  Purchase #4 $247.69   11.275%   $275.617   $275.62   $275.60   $275.60  
  Purchase #5 $241.77   9.670%   $265.1492   $265.15   $265.15   $265.10  
  Purchase #6 $249.89   5.458%   $263.529   $263.53   $263.55   $263.50  
  Purchase #7 $105.44   4.220%   $109.8896   $109.89   $109.90   $109.90  
  7 purchase totals = $1,302.82       $1,420.9004   $1,420.91   $1,420.90   $1,420.80