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 $48.63   13.308%   $55.1017   $55.10   $55.10   $55.10  
  Purchase #2 $58.95   3.379%   $60.9419   $60.94   $60.95   $60.90  
  Purchase #3 $133.81   6.297%   $142.236   $142.24   $142.25   $142.20  
  Purchase #4 $234.37   10.170%   $258.2054   $258.21   $258.20   $258.20  
  Purchase #5 $62.79   3.853%   $65.2093   $65.21   $65.20   $65.20  
  Purchase #6 $124.67   5.816%   $131.9208   $131.92   $131.90   $131.90  
  Purchase #7 $170.95   6.619%   $182.2652   $182.27   $182.25   $182.30  
  7 purchase totals = $834.17       $895.8803   $895.89   $895.85   $895.80