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 $82.95   12.868%   $93.624   $93.62   $93.60   $93.60  
  Purchase #2 $139.75   5.165%   $146.9681   $146.97   $146.95   $147.00  
  Purchase #3 $22.98   5.754%   $24.3023   $24.30   $24.30   $24.30  
  Purchase #4 $177.35   6.276%   $188.4805   $188.48   $188.50   $188.50  
  Purchase #5 $64.63   10.422%   $71.3657   $71.37   $71.35   $71.40  
  Purchase #6 $217.87   8.119%   $235.5589   $235.56   $235.55   $235.60  
  Purchase #7 $14.46   5.679%   $15.2812   $15.28   $15.30   $15.30  
  7 purchase totals = $719.99       $775.5807   $775.58   $775.55   $775.70