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 $44.44   13.405%   $50.3972   $50.40   $50.40   $50.40  
  Purchase #2 $61.63   3.842%   $63.9978   $64.00   $64.00   $64.00  
  Purchase #3 $133.73   13.293%   $151.5067   $151.51   $151.50   $151.50  
  Purchase #4 $120.50   11.432%   $134.2756   $134.28   $134.30   $134.30  
  Purchase #5 $176.98   3.699%   $183.5265   $183.53   $183.55   $183.50  
  Purchase #6 $194.90   10.623%   $215.6042   $215.60   $215.60   $215.60  
  Purchase #7 $69.77   4.122%   $72.6459   $72.65   $72.65   $72.60  
  7 purchase totals = $801.95       $871.9539   $871.97   $872.00   $871.90