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 $59.83   5.836%   $63.3217   $63.32   $63.30   $63.30  
  Purchase #2 $65.82   8.825%   $71.6286   $71.63   $71.65   $71.60  
  Purchase #3 $247.67   4.349%   $258.4412   $258.44   $258.45   $258.40  
  Purchase #4 $214.44   6.151%   $227.6302   $227.63   $227.65   $227.60  
  Purchase #5 $118.73   6.758%   $126.7538   $126.75   $126.75   $126.80  
  Purchase #6 $68.34   9.727%   $74.9874   $74.99   $75.00   $75.00  
  Purchase #7 $246.47   3.719%   $255.6362   $255.64   $255.65   $255.60  
  7 purchase totals = $1,021.30       $1,078.3991   $1,078.40   $1,078.45   $1,078.30