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 $62.98   9.621%   $69.0393   $69.04   $69.05   $69.00  
  Purchase #2 $53.43   7.812%   $57.604   $57.60   $57.60   $57.60  
  Purchase #3 $192.88   8.776%   $209.8071   $209.81   $209.80   $209.80  
  Purchase #4 $58.91   9.811%   $64.6897   $64.69   $64.70   $64.70  
  Purchase #5 $101.61   8.382%   $110.127   $110.13   $110.15   $110.10  
  Purchase #6 $207.34   4.697%   $217.0788   $217.08   $217.10   $217.10  
  Purchase #7 $154.66   3.845%   $160.6067   $160.61   $160.60   $160.60  
  7 purchase totals = $831.81       $888.9526   $888.96   $889.00   $888.90