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 $93.67   4.333%   $97.7287   $97.73   $97.75   $97.70  
  Purchase #2 $69.46   10.716%   $76.9033   $76.90   $76.90   $76.90  
  Purchase #3 $241.59   11.185%   $268.6118   $268.61   $268.60   $268.60  
  Purchase #4 $149.42   9.257%   $163.2518   $163.25   $163.25   $163.30  
  Purchase #5 $133.39   6.127%   $141.5628   $141.56   $141.55   $141.60  
  Purchase #6 $61.54   6.554%   $65.5733   $65.57   $65.55   $65.60  
  Purchase #7 $20.96   4.866%   $21.9799   $21.98   $22.00   $22.00  
  7 purchase totals = $770.03       $835.6116   $835.60   $835.60   $835.70