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 $52.62   13.318%   $59.6279   $59.63   $59.65   $59.60  
  Purchase #2 $152.73   8.186%   $165.2325   $165.23   $165.25   $165.20  
  Purchase #3 $128.45   5.306%   $135.2656   $135.27   $135.25   $135.30  
  Purchase #4 $241.81   5.753%   $255.7213   $255.72   $255.70   $255.70  
  Purchase #5 $87.52   5.866%   $92.6539   $92.65   $92.65   $92.70  
  Purchase #6 $44.68   12.406%   $50.223   $50.22   $50.20   $50.20  
  Purchase #7 $106.25   9.172%   $115.9953   $116.00   $116.00   $116.00  
  7 purchase totals = $814.06       $874.7195   $874.72   $874.70   $874.70