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 $242.44   10.767%   $268.5435   $268.54   $268.55   $268.50  
  Purchase #2 $144.96   5.321%   $152.6733   $152.67   $152.65   $152.70  
  Purchase #3 $6.98   4.596%   $7.3008   $7.30   $7.30   $7.30  
  Purchase #4 $199.68   5.803%   $211.2674   $211.27   $211.25   $211.30  
  Purchase #5 $18.58   11.458%   $20.7089   $20.71   $20.70   $20.70  
  Purchase #6 $58.84   12.121%   $65.972   $65.97   $65.95   $66.00  
  Purchase #7 $69.82   9.362%   $76.3565   $76.36   $76.35   $76.40  
  7 purchase totals = $741.30       $802.8224   $802.82   $802.75   $802.90