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 $53.97   12.113%   $60.5074   $60.51   $60.50   $60.50  
  Purchase #2 $170.59   11.868%   $190.8356   $190.84   $190.85   $190.80  
  Purchase #3 $241.36   6.704%   $257.5408   $257.54   $257.55   $257.50  
  Purchase #4 $10.68   11.664%   $11.9257   $11.93   $11.95   $11.90  
  Purchase #5 $65.89   11.741%   $73.6261   $73.63   $73.65   $73.60  
  Purchase #6 $94.51   11.550%   $105.4259   $105.43   $105.45   $105.40  
  Purchase #7 $48.94   12.466%   $55.0409   $55.04   $55.05   $55.00  
  7 purchase totals = $685.94       $754.9024   $754.92   $755.00   $754.70