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 $62.84   10.127%   $69.2038   $69.20   $69.20   $69.20  
  Purchase #2 $238.76   11.358%   $265.8784   $265.88   $265.90   $265.90  
  Purchase #3 $118.28   11.831%   $132.2737   $132.27   $132.25   $132.30  
  Purchase #4 $11.40   5.366%   $12.0117   $12.01   $12.00   $12.00  
  Purchase #5 $8.71   8.222%   $9.4261   $9.43   $9.45   $9.40  
  Purchase #6 $141.97   11.432%   $158.2   $158.20   $158.20   $158.20  
  Purchase #7 $49.31   8.480%   $53.4915   $53.49   $53.50   $53.50  
  7 purchase totals = $631.27       $700.4852   $700.48   $700.50   $700.50