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 $118.95   11.809%   $132.9968   $133.00   $133.00   $133.00  
  Purchase #2 $112.82   6.509%   $120.1635   $120.16   $120.15   $120.20  
  Purchase #3 $214.76   7.673%   $231.2385   $231.24   $231.25   $231.20  
  Purchase #4 $187.48   3.790%   $194.5855   $194.59   $194.60   $194.60  
  Purchase #5 $216.45   12.271%   $243.0106   $243.01   $243.00   $243.00  
  Purchase #6 $229.83   11.573%   $256.4282   $256.43   $256.45   $256.40  
  Purchase #7 $42.76   5.171%   $44.9711   $44.97   $44.95   $45.00  
  7 purchase totals = $1,123.05       $1,223.3942   $1,223.40   $1,223.40   $1,223.40