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 $149.55   8.434%   $162.163   $162.16   $162.15   $162.20  
  Purchase #2 $112.82   8.276%   $122.157   $122.16   $122.15   $122.20  
  Purchase #3 $113.38   5.734%   $119.8812   $119.88   $119.90   $119.90  
  Purchase #4 $81.79   7.703%   $88.0903   $88.09   $88.10   $88.10  
  Purchase #5 $227.67   13.532%   $258.4783   $258.48   $258.50   $258.50  
  Purchase #6 $205.48   10.763%   $227.5958   $227.60   $227.60   $227.60  
  Purchase #7 $64.29   7.614%   $69.185   $69.19   $69.20   $69.20  
  7 purchase totals = $954.98       $1,047.5506   $1,047.56   $1,047.60   $1,047.70