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 $32.35   12.435%   $36.3727   $36.37   $36.35   $36.40  
  Purchase #2 $36.98   10.804%   $40.9753   $40.98   $41.00   $41.00  
  Purchase #3 $205.27   13.169%   $232.302   $232.30   $232.30   $232.30  
  Purchase #4 $132.72   6.438%   $141.2645   $141.26   $141.25   $141.30  
  Purchase #5 $100.85   3.784%   $104.6662   $104.67   $104.65   $104.70  
  Purchase #6 $232.68   7.185%   $249.3981   $249.40   $249.40   $249.40  
  Purchase #7 $69.96   10.597%   $77.3737   $77.37   $77.35   $77.40  
  7 purchase totals = $810.81       $882.3525   $882.35   $882.30   $882.50