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 $215.72   5.104%   $226.7303   $226.73   $226.75   $226.70  
  Purchase #2 $140.65   6.395%   $149.6446   $149.64   $149.65   $149.60  
  Purchase #3 $210.66   6.548%   $224.454   $224.45   $224.45   $224.50  
  Purchase #4 $87.76   9.846%   $96.4008   $96.40   $96.40   $96.40  
  Purchase #5 $34.80   13.164%   $39.3811   $39.38   $39.40   $39.40  
  Purchase #6 $39.27   13.634%   $44.6241   $44.62   $44.60   $44.60  
  Purchase #7 $213.38   9.134%   $232.8701   $232.87   $232.85   $232.90  
  7 purchase totals = $942.24       $1,014.1050   $1,014.09   $1,014.10   $1,014.10