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 $131.39   7.377%   $141.0826   $141.08   $141.10   $141.10  
  Purchase #2 $235.91   10.828%   $261.4543   $261.45   $261.45   $261.50  
  Purchase #3 $35.47   3.800%   $36.8179   $36.82   $36.80   $36.80  
  Purchase #4 $62.36   3.794%   $64.7259   $64.73   $64.75   $64.70  
  Purchase #5 $52.70   10.204%   $58.0775   $58.08   $58.10   $58.10  
  Purchase #6 $24.63   3.566%   $25.5083   $25.51   $25.50   $25.50  
  Purchase #7 $210.52   4.821%   $220.6692   $220.67   $220.65   $220.70  
  7 purchase totals = $752.98       $808.3357   $808.34   $808.35   $808.40