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 $60.43   8.480%   $65.5545   $65.55   $65.55   $65.60  
  Purchase #2 $217.46   7.503%   $233.776   $233.78   $233.80   $233.80  
  Purchase #3 $116.52   11.152%   $129.5143   $129.51   $129.50   $129.50  
  Purchase #4 $212.53   4.344%   $221.7623   $221.76   $221.75   $221.80  
  Purchase #5 $152.99   3.342%   $158.1029   $158.10   $158.10   $158.10  
  Purchase #6 $162.50   9.258%   $177.5443   $177.54   $177.55   $177.50  
  Purchase #7 $42.94   13.222%   $48.6175   $48.62   $48.60   $48.60  
  7 purchase totals = $965.37       $1,034.8718   $1,034.86   $1,034.85   $1,034.90