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 $208.37   6.265%   $221.4244   $221.42   $221.40   $221.40  
  Purchase #2 $197.97   9.532%   $216.8405   $216.84   $216.85   $216.80  
  Purchase #3 $58.52   7.809%   $63.0898   $63.09   $63.10   $63.10  
  Purchase #4 $129.59   5.245%   $136.387   $136.39   $136.40   $136.40  
  Purchase #5 $177.38   7.544%   $190.7615   $190.76   $190.75   $190.80  
  Purchase #6 $230.92   9.642%   $253.1853   $253.19   $253.20   $253.20  
  Purchase #7 $250.25   5.103%   $263.0203   $263.02   $263.00   $263.00  
  7 purchase totals = $1,253.00       $1,344.7088   $1,344.71   $1,344.70   $1,344.70