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 $68.57   12.207%   $76.9403   $76.94   $76.95   $76.90  
  Purchase #2 $23.76   10.276%   $26.2016   $26.20   $26.20   $26.20  
  Purchase #3 $68.44   11.617%   $76.3907   $76.39   $76.40   $76.40  
  Purchase #4 $88.54   12.518%   $99.6234   $99.62   $99.60   $99.60  
  Purchase #5 $210.50   11.344%   $234.3791   $234.38   $234.40   $234.40  
  Purchase #6 $161.48   11.530%   $180.0986   $180.10   $180.10   $180.10  
  Purchase #7 $41.35   8.297%   $44.7808   $44.78   $44.80   $44.80  
  7 purchase totals = $662.64       $738.4145   $738.41   $738.45   $738.40