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 $88.62   8.154%   $95.8461   $95.85   $95.85   $95.80  
  Purchase #2 $71.55   5.733%   $75.652   $75.65   $75.65   $75.70  
  Purchase #3 $199.47   12.759%   $224.9204   $224.92   $224.90   $224.90  
  Purchase #4 $7.99   5.226%   $8.4076   $8.41   $8.40   $8.40  
  Purchase #5 $250.34   12.168%   $280.8014   $280.80   $280.80   $280.80  
  Purchase #6 $59.61   9.224%   $65.1084   $65.11   $65.10   $65.10  
  Purchase #7 $43.50   5.782%   $46.0152   $46.02   $46.00   $46.00  
  7 purchase totals = $721.08       $796.7511   $796.76   $796.70   $796.70