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 $55.84   4.377%   $58.2841   $58.28   $58.30   $58.30  
  Purchase #2 $151.37   10.786%   $167.6968   $167.70   $167.70   $167.70  
  Purchase #3 $117.52   12.740%   $132.492   $132.49   $132.50   $132.50  
  Purchase #4 $41.89   11.550%   $46.7283   $46.73   $46.75   $46.70  
  Purchase #5 $84.58   12.816%   $95.4198   $95.42   $95.40   $95.40  
  Purchase #6 $134.73   12.811%   $151.9903   $151.99   $152.00   $152.00  
  Purchase #7 $173.94   5.522%   $183.545   $183.55   $183.55   $183.50  
  7 purchase totals = $759.87       $836.1563   $836.16   $836.20   $836.10