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 $110.72   6.569%   $117.9932   $117.99   $118.00   $118.00  
  Purchase #2 $229.68   13.268%   $260.1539   $260.15   $260.15   $260.20  
  Purchase #3 $216.98   9.325%   $237.2134   $237.21   $237.20   $237.20  
  Purchase #4 $46.73   10.596%   $51.6815   $51.68   $51.70   $51.70  
  Purchase #5 $42.28   12.643%   $47.6255   $47.63   $47.65   $47.60  
  Purchase #6 $61.44   9.330%   $67.1724   $67.17   $67.15   $67.20  
  Purchase #7 $95.32   8.118%   $103.0581   $103.06   $103.05   $103.10  
  7 purchase totals = $803.15       $884.8980   $884.89   $884.90   $885.00