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 $53.85   11.683%   $60.1413   $60.14   $60.15   $60.10  
  Purchase #2 $116.84   13.191%   $132.2524   $132.25   $132.25   $132.30  
  Purchase #3 $82.42   11.277%   $91.7145   $91.71   $91.70   $91.70  
  Purchase #4 $207.77   13.422%   $235.6569   $235.66   $235.65   $235.70  
  Purchase #5 $167.42   13.430%   $189.9045   $189.90   $189.90   $189.90  
  Purchase #6 $108.70   11.546%   $121.2505   $121.25   $121.25   $121.30  
  Purchase #7 $109.29   6.108%   $115.9654   $115.97   $115.95   $116.00  
  7 purchase totals = $846.29       $946.8855   $946.88   $946.85   $947.00