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 $94.46   4.851%   $99.0423   $99.04   $99.05   $99.00  
  Purchase #2 $140.97   3.785%   $146.3057   $146.31   $146.30   $146.30  
  Purchase #3 $84.62   12.137%   $94.8903   $94.89   $94.90   $94.90  
  Purchase #4 $208.64   13.463%   $236.7292   $236.73   $236.75   $236.70  
  Purchase #5 $202.87   9.426%   $221.9925   $221.99   $222.00   $222.00  
  Purchase #6 $54.95   12.828%   $61.999   $62.00   $62.00   $62.00  
  Purchase #7 $91.94   4.245%   $95.8429   $95.84   $95.85   $95.80  
  7 purchase totals = $878.45       $956.8019   $956.80   $956.85   $956.70