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 $68.42   9.477%   $74.9042   $74.90   $74.90   $74.90  
  Purchase #2 $170.53   10.670%   $188.7256   $188.73   $188.75   $188.70  
  Purchase #3 $120.76   9.658%   $132.423   $132.42   $132.40   $132.40  
  Purchase #4 $210.57   3.266%   $217.4472   $217.45   $217.45   $217.40  
  Purchase #5 $176.96   7.821%   $190.8   $190.80   $190.80   $190.80  
  Purchase #6 $49.73   9.738%   $54.5727   $54.57   $54.55   $54.60  
  Purchase #7 $245.99   6.709%   $262.4935   $262.49   $262.50   $262.50  
  7 purchase totals = $1,042.96       $1,121.3662   $1,121.36   $1,121.35   $1,121.30