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 $88.83   10.276%   $97.9582   $97.96   $97.95   $98.00  
  Purchase #2 $130.44   8.580%   $141.6318   $141.63   $141.65   $141.60  
  Purchase #3 $16.44   6.137%   $17.4489   $17.45   $17.45   $17.40  
  Purchase #4 $229.37   4.339%   $239.3224   $239.32   $239.30   $239.30  
  Purchase #5 $144.75   9.596%   $158.6402   $158.64   $158.65   $158.60  
  Purchase #6 $151.80   12.734%   $171.1302   $171.13   $171.15   $171.10  
  Purchase #7 $60.82   4.566%   $63.597   $63.60   $63.60   $63.60  
  7 purchase totals = $822.45       $889.7287   $889.73   $889.75   $889.60