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 $21.40   3.472%   $22.143   $22.14   $22.15   $22.10  
  Purchase #2 $138.99   9.625%   $152.3678   $152.37   $152.35   $152.40  
  Purchase #3 $183.72   5.870%   $194.5044   $194.50   $194.50   $194.50  
  Purchase #4 $100.71   3.425%   $104.1593   $104.16   $104.15   $104.20  
  Purchase #5 $235.40   4.764%   $246.6145   $246.61   $246.60   $246.60  
  Purchase #6 $91.97   6.424%   $97.8782   $97.88   $97.90   $97.90  
  Purchase #7 $114.27   6.463%   $121.6553   $121.66   $121.65   $121.70  
  7 purchase totals = $886.46       $939.3225   $939.32   $939.30   $939.40