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 $58.72   10.731%   $65.0212   $65.02   $65.00   $65.00  
  Purchase #2 $190.58   13.845%   $216.9658   $216.97   $216.95   $217.00  
  Purchase #3 $194.78   11.626%   $217.4251   $217.43   $217.45   $217.40  
  Purchase #4 $139.57   3.249%   $144.1046   $144.10   $144.10   $144.10  
  Purchase #5 $187.39   11.792%   $209.487   $209.49   $209.50   $209.50  
  Purchase #6 $56.34   4.247%   $58.7328   $58.73   $58.75   $58.70  
  Purchase #7 $146.86   10.863%   $162.8134   $162.81   $162.80   $162.80  
  7 purchase totals = $974.24       $1,074.5499   $1,074.55   $1,074.55   $1,074.50