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 $46.97   5.786%   $49.6877   $49.69   $49.70   $49.70  
  Purchase #2 $211.96   3.792%   $219.9975   $220.00   $220.00   $220.00  
  Purchase #3 $33.93   13.118%   $38.3809   $38.38   $38.40   $38.40  
  Purchase #4 $21.38   12.836%   $24.1243   $24.12   $24.10   $24.10  
  Purchase #5 $161.61   10.578%   $178.7051   $178.71   $178.70   $178.70  
  Purchase #6 $62.29   11.790%   $69.634   $69.63   $69.65   $69.60  
  Purchase #7 $231.45   12.805%   $261.0872   $261.09   $261.10   $261.10  
  7 purchase totals = $769.59       $841.6167   $841.62   $841.65   $841.60