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 $70.26   6.377%   $74.7405   $74.74   $74.75   $74.70  
  Purchase #2 $209.93   13.508%   $238.2873   $238.29   $238.30   $238.30  
  Purchase #3 $53.64   8.665%   $58.2879   $58.29   $58.30   $58.30  
  Purchase #4 $13.38   8.859%   $14.5653   $14.57   $14.55   $14.60  
  Purchase #5 $73.40   10.509%   $81.1136   $81.11   $81.10   $81.10  
  Purchase #6 $246.98   10.546%   $273.0265   $273.03   $273.05   $273.00  
  Purchase #7 $14.51   12.157%   $16.274   $16.27   $16.25   $16.30  
  7 purchase totals = $682.10       $756.2951   $756.30   $756.30   $756.30