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 $207.53   12.282%   $233.0188   $233.02   $233.00   $233.00  
  Purchase #2 $156.65   5.507%   $165.2767   $165.28   $165.30   $165.30  
  Purchase #3 $205.63   5.703%   $217.3571   $217.36   $217.35   $217.40  
  Purchase #4 $13.55   6.403%   $14.4176   $14.42   $14.40   $14.40  
  Purchase #5 $111.62   6.587%   $118.9724   $118.97   $118.95   $119.00  
  Purchase #6 $135.48   11.140%   $150.5725   $150.57   $150.55   $150.60  
  Purchase #7 $89.82   13.114%   $101.599   $101.60   $101.60   $101.60  
  7 purchase totals = $920.28       $1,001.2141   $1,001.22   $1,001.15   $1,001.30