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 $84.65   4.799%   $88.7124   $88.71   $88.70   $88.70  
  Purchase #2 $127.29   4.362%   $132.8424   $132.84   $132.85   $132.80  
  Purchase #3 $160.51   13.725%   $182.54   $182.54   $182.55   $182.50  
  Purchase #4 $134.93   12.228%   $151.4292   $151.43   $151.45   $151.40  
  Purchase #5 $242.76   9.463%   $265.7324   $265.73   $265.75   $265.70  
  Purchase #6 $151.37   4.495%   $158.1741   $158.17   $158.15   $158.20  
  Purchase #7 $141.83   10.689%   $156.9902   $156.99   $157.00   $157.00  
  7 purchase totals = $1,043.34       $1,136.4207   $1,136.41   $1,136.45   $1,136.30