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 $114.53   11.533%   $127.7387   $127.74   $127.75   $127.70  
  Purchase #2 $85.37   12.676%   $96.1915   $96.19   $96.20   $96.20  
  Purchase #3 $25.31   5.102%   $26.6013   $26.60   $26.60   $26.60  
  Purchase #4 $157.67   7.282%   $169.1515   $169.15   $169.15   $169.20  
  Purchase #5 $234.58   9.260%   $256.3021   $256.30   $256.30   $256.30  
  Purchase #6 $221.64   11.354%   $246.805   $246.81   $246.80   $246.80  
  Purchase #7 $48.72   4.131%   $50.7326   $50.73   $50.75   $50.70  
  7 purchase totals = $887.82       $973.5227   $973.52   $973.55   $973.50