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 $62.39   12.132%   $69.9592   $69.96   $69.95   $70.00  
  Purchase #2 $116.61   4.873%   $122.2924   $122.29   $122.30   $122.30  
  Purchase #3 $230.87   10.776%   $255.7486   $255.75   $255.75   $255.70  
  Purchase #4 $105.47   11.583%   $117.6866   $117.69   $117.70   $117.70  
  Purchase #5 $186.39   12.383%   $209.4707   $209.47   $209.45   $209.50  
  Purchase #6 $49.48   4.386%   $51.6502   $51.65   $51.65   $51.70  
  Purchase #7 $21.78   13.220%   $24.6593   $24.66   $24.65   $24.70  
  7 purchase totals = $772.99       $851.4670   $851.47   $851.45   $851.60