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 $67.98   12.779%   $76.6672   $76.67   $76.65   $76.70  
  Purchase #2 $110.36   11.179%   $122.6971   $122.70   $122.70   $122.70  
  Purchase #3 $229.72   13.274%   $260.213   $260.21   $260.20   $260.20  
  Purchase #4 $189.48   6.208%   $201.2429   $201.24   $201.25   $201.20  
  Purchase #5 $79.63   7.421%   $85.5393   $85.54   $85.55   $85.50  
  Purchase #6 $144.84   7.688%   $155.9753   $155.98   $156.00   $156.00  
  Purchase #7 $150.47   5.567%   $158.8467   $158.85   $158.85   $158.80  
  7 purchase totals = $972.48       $1,061.1815   $1,061.19   $1,061.20   $1,061.10