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 $75.32   11.481%   $83.9675   $83.97   $83.95   $84.00  
  Purchase #2 $45.78   3.533%   $47.3974   $47.40   $47.40   $47.40  
  Purchase #3 $104.82   5.519%   $110.605   $110.61   $110.60   $110.60  
  Purchase #4 $200.47   3.210%   $206.9051   $206.91   $206.90   $206.90  
  Purchase #5 $124.50   11.488%   $138.8026   $138.80   $138.80   $138.80  
  Purchase #6 $83.33   8.464%   $90.3831   $90.38   $90.40   $90.40  
  Purchase #7 $98.74   6.340%   $105.0001   $105.00   $105.00   $105.00  
  7 purchase totals = $732.96       $783.0608   $783.07   $783.05   $783.10