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 $207.57   10.697%   $229.7738   $229.77   $229.75   $229.80  
  Purchase #2 $109.92   6.228%   $116.7658   $116.77   $116.75   $116.80  
  Purchase #3 $35.65   4.302%   $37.1837   $37.18   $37.20   $37.20  
  Purchase #4 $205.89   6.306%   $218.8734   $218.87   $218.85   $218.90  
  Purchase #5 $34.86   12.499%   $39.2172   $39.22   $39.20   $39.20  
  Purchase #6 $222.76   8.627%   $241.9775   $241.98   $242.00   $242.00  
  Purchase #7 $65.48   11.454%   $72.9801   $72.98   $73.00   $73.00  
  7 purchase totals = $882.13       $956.7715   $956.77   $956.75   $956.90