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 $210.70   3.239%   $217.5246   $217.52   $217.50   $217.50  
  Purchase #2 $86.35   11.431%   $96.2207   $96.22   $96.20   $96.20  
  Purchase #3 $55.80   5.736%   $59.0007   $59.00   $59.00   $59.00  
  Purchase #4 $113.43   8.858%   $123.4776   $123.48   $123.50   $123.50  
  Purchase #5 $159.25   6.831%   $170.1284   $170.13   $170.15   $170.10  
  Purchase #6 $40.64   11.213%   $45.197   $45.20   $45.20   $45.20  
  Purchase #7 $220.34   8.808%   $239.7475   $239.75   $239.75   $239.70  
  7 purchase totals = $886.51       $951.2965   $951.30   $951.30   $951.20