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 $48.98   7.241%   $52.5266   $52.53   $52.55   $52.50  
  Purchase #2 $70.39   13.262%   $79.7251   $79.73   $79.75   $79.70  
  Purchase #3 $164.29   4.500%   $171.6831   $171.68   $171.70   $171.70  
  Purchase #4 $146.87   13.324%   $166.439   $166.44   $166.45   $166.40  
  Purchase #5 $83.36   12.463%   $93.7492   $93.75   $93.75   $93.70  
  Purchase #6 $25.87   5.443%   $27.2781   $27.28   $27.30   $27.30  
  Purchase #7 $198.43   7.571%   $213.4531   $213.45   $213.45   $213.50  
  7 purchase totals = $738.19       $804.8542   $804.86   $804.95   $804.80