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 $19.54   6.309%   $20.7728   $20.77   $20.75   $20.80  
  Purchase #2 $15.51   3.776%   $16.0957   $16.10   $16.10   $16.10  
  Purchase #3 $74.29   3.796%   $77.11   $77.11   $77.10   $77.10  
  Purchase #4 $104.94   4.847%   $110.0264   $110.03   $110.05   $110.00  
  Purchase #5 $88.63   10.825%   $98.2242   $98.22   $98.20   $98.20  
  Purchase #6 $62.48   11.683%   $69.7795   $69.78   $69.80   $69.80  
  Purchase #7 $116.86   4.275%   $121.8558   $121.86   $121.85   $121.90  
  7 purchase totals = $482.25       $513.8644   $513.87   $513.85   $513.90