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 $241.36   8.359%   $261.5353   $261.54   $261.55   $261.50  
  Purchase #2 $59.75   4.807%   $62.6222   $62.62   $62.60   $62.60  
  Purchase #3 $23.76   6.700%   $25.3519   $25.35   $25.35   $25.40  
  Purchase #4 $216.63   11.573%   $241.7006   $241.70   $241.70   $241.70  
  Purchase #5 $11.47   4.623%   $12.0003   $12.00   $12.00   $12.00  
  Purchase #6 $126.40   8.553%   $137.211   $137.21   $137.20   $137.20  
  Purchase #7 $105.93   4.464%   $110.6587   $110.66   $110.65   $110.70  
  7 purchase totals = $785.30       $851.0800   $851.08   $851.05   $851.10