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 $31.56   9.220%   $34.4698   $34.47   $34.45   $34.50  
  Purchase #2 $159.36   4.763%   $166.9503   $166.95   $166.95   $167.00  
  Purchase #3 $185.42   5.643%   $195.8833   $195.88   $195.90   $195.90  
  Purchase #4 $73.40   4.530%   $76.725   $76.73   $76.75   $76.70  
  Purchase #5 $187.59   6.701%   $200.1604   $200.16   $200.15   $200.20  
  Purchase #6 $77.39   13.637%   $87.9437   $87.94   $87.95   $87.90  
  Purchase #7 $122.54   3.446%   $126.7627   $126.76   $126.75   $126.80  
  7 purchase totals = $837.26       $888.8952   $888.89   $888.90   $889.00