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 $229.37   10.628%   $253.7474   $253.75   $253.75   $253.70  
  Purchase #2 $86.93   11.165%   $96.6357   $96.64   $96.65   $96.60  
  Purchase #3 $73.98   5.208%   $77.8329   $77.83   $77.85   $77.80  
  Purchase #4 $9.52   7.379%   $10.2225   $10.22   $10.20   $10.20  
  Purchase #5 $205.54   6.267%   $218.4212   $218.42   $218.40   $218.40  
  Purchase #6 $32.28   12.187%   $36.214   $36.21   $36.20   $36.20  
  Purchase #7 $59.89   7.358%   $64.2967   $64.30   $64.30   $64.30  
  7 purchase totals = $697.51       $757.3704   $757.37   $757.35   $757.20