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 $46.93   10.137%   $51.6873   $51.69   $51.70   $51.70  
  Purchase #2 $105.45   7.596%   $113.46   $113.46   $113.45   $113.50  
  Purchase #3 $69.62   13.459%   $78.9902   $78.99   $79.00   $79.00  
  Purchase #4 $7.72   13.219%   $8.7405   $8.74   $8.75   $8.70  
  Purchase #5 $219.59   12.491%   $247.019   $247.02   $247.00   $247.00  
  Purchase #6 $93.73   4.522%   $97.9685   $97.97   $97.95   $98.00  
  Purchase #7 $58.64   10.542%   $64.8218   $64.82   $64.80   $64.80  
  7 purchase totals = $601.68       $662.6873   $662.69   $662.65   $662.70