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 $84.81   12.305%   $95.2459   $95.25   $95.25   $95.20  
  Purchase #2 $155.53   10.196%   $171.3878   $171.39   $171.40   $171.40  
  Purchase #3 $234.99   8.459%   $254.8678   $254.87   $254.85   $254.90  
  Purchase #4 $247.65   5.159%   $260.4263   $260.43   $260.45   $260.40  
  Purchase #5 $25.78   7.413%   $27.6911   $27.69   $27.70   $27.70  
  Purchase #6 $29.36   8.698%   $31.9137   $31.91   $31.90   $31.90  
  Purchase #7 $70.76   8.742%   $76.9458   $76.95   $76.95   $76.90  
  7 purchase totals = $848.88       $918.4784   $918.49   $918.50   $918.40