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 $58.54   13.555%   $66.4751   $66.48   $66.50   $66.50  
  Purchase #2 $139.62   9.293%   $152.5949   $152.59   $152.60   $152.60  
  Purchase #3 $56.57   5.288%   $59.5614   $59.56   $59.55   $59.60  
  Purchase #4 $224.62   5.735%   $237.502   $237.50   $237.50   $237.50  
  Purchase #5 $109.63   3.414%   $113.3728   $113.37   $113.35   $113.40  
  Purchase #6 $132.71   4.303%   $138.4205   $138.42   $138.40   $138.40  
  Purchase #7 $248.51   4.355%   $259.3326   $259.33   $259.35   $259.30  
  7 purchase totals = $970.20       $1,027.2593   $1,027.25   $1,027.25   $1,027.30