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 $52.89   7.545%   $56.8806   $56.88   $56.90   $56.90  
  Purchase #2 $63.97   6.323%   $68.0148   $68.01   $68.00   $68.00  
  Purchase #3 $195.73   7.607%   $210.6192   $210.62   $210.60   $210.60  
  Purchase #4 $52.89   13.868%   $60.2248   $60.22   $60.20   $60.20  
  Purchase #5 $126.31   4.871%   $132.4626   $132.46   $132.45   $132.50  
  Purchase #6 $171.93   6.194%   $182.5793   $182.58   $182.60   $182.60  
  Purchase #7 $194.83   5.319%   $205.193   $205.19   $205.20   $205.20  
  7 purchase totals = $858.55       $915.9743   $915.96   $915.95   $916.00