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 $247.47   11.321%   $275.4861   $275.49   $275.50   $275.50  
  Purchase #2 $92.88   12.778%   $104.7482   $104.75   $104.75   $104.70  
  Purchase #3 $160.77   8.150%   $173.8728   $173.87   $173.85   $173.90  
  Purchase #4 $170.48   6.792%   $182.059   $182.06   $182.05   $182.10  
  Purchase #5 $210.46   8.796%   $228.9721   $228.97   $228.95   $229.00  
  Purchase #6 $140.98   6.528%   $150.1832   $150.18   $150.20   $150.20  
  Purchase #7 $213.76   13.248%   $242.0789   $242.08   $242.10   $242.10  
  7 purchase totals = $1,236.80       $1,357.4003   $1,357.40   $1,357.40   $1,357.50