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 $43.29   11.378%   $48.2155   $48.22   $48.20   $48.20  
  Purchase #2 $223.53   8.633%   $242.8273   $242.83   $242.85   $242.80  
  Purchase #3 $209.44   5.686%   $221.3488   $221.35   $221.35   $221.30  
  Purchase #4 $238.52   12.259%   $267.7602   $267.76   $267.75   $267.80  
  Purchase #5 $82.55   10.602%   $91.302   $91.30   $91.30   $91.30  
  Purchase #6 $117.98   10.614%   $130.5024   $130.50   $130.50   $130.50  
  Purchase #7 $168.73   4.138%   $175.712   $175.71   $175.70   $175.70  
  7 purchase totals = $1,084.04       $1,177.6682   $1,177.67   $1,177.65   $1,177.60