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 $32.47   5.660%   $34.3078   $34.31   $34.30   $34.30  
  Purchase #2 $115.64   6.791%   $123.4931   $123.49   $123.50   $123.50  
  Purchase #3 $17.28   3.626%   $17.9066   $17.91   $17.90   $17.90  
  Purchase #4 $139.67   6.309%   $148.4818   $148.48   $148.50   $148.50  
  Purchase #5 $113.51   5.454%   $119.7008   $119.70   $119.70   $119.70  
  Purchase #6 $103.74   8.260%   $112.3089   $112.31   $112.30   $112.30  
  Purchase #7 $246.96   5.337%   $260.1403   $260.14   $260.15   $260.10  
  7 purchase totals = $769.27       $816.3393   $816.34   $816.35   $816.30