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 $227.59   8.169%   $246.1818   $246.18   $246.20   $246.20  
  Purchase #2 $194.51   13.764%   $221.2824   $221.28   $221.30   $221.30  
  Purchase #3 $151.42   5.829%   $160.2463   $160.25   $160.25   $160.20  
  Purchase #4 $194.41   4.730%   $203.6056   $203.61   $203.60   $203.60  
  Purchase #5 $208.84   13.714%   $237.4803   $237.48   $237.50   $237.50  
  Purchase #6 $213.25   12.530%   $239.9702   $239.97   $239.95   $240.00  
  Purchase #7 $46.43   5.237%   $48.8615   $48.86   $48.85   $48.90  
  7 purchase totals = $1,236.45       $1,357.6281   $1,357.63   $1,357.65   $1,357.70