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 $124.76   10.843%   $138.2877   $138.29   $138.30   $138.30  
  Purchase #2 $98.29   7.141%   $105.3089   $105.31   $105.30   $105.30  
  Purchase #3 $34.46   8.488%   $37.385   $37.39   $37.40   $37.40  
  Purchase #4 $19.75   9.805%   $21.6865   $21.69   $21.70   $21.70  
  Purchase #5 $191.67   5.314%   $201.8553   $201.86   $201.85   $201.90  
  Purchase #6 $158.79   6.626%   $169.3114   $169.31   $169.30   $169.30  
  Purchase #7 $68.72   9.207%   $75.0471   $75.05   $75.05   $75.00  
  7 purchase totals = $696.44       $748.8819   $748.90   $748.90   $748.90