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 $205.45   5.194%   $216.1211   $216.12   $216.10   $216.10  
  Purchase #2 $117.83   13.821%   $134.1153   $134.12   $134.10   $134.10  
  Purchase #3 $212.41   13.700%   $241.5102   $241.51   $241.50   $241.50  
  Purchase #4 $92.82   12.281%   $104.2192   $104.22   $104.20   $104.20  
  Purchase #5 $54.95   10.828%   $60.9   $60.90   $60.90   $60.90  
  Purchase #6 $5.94   6.358%   $6.3177   $6.32   $6.30   $6.30  
  Purchase #7 $18.42   3.374%   $19.0415   $19.04   $19.05   $19.00  
  7 purchase totals = $707.82       $782.2250   $782.23   $782.15   $782.10