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 $29.64   12.132%   $33.2359   $33.24   $33.25   $33.20  
  Purchase #2 $189.96   4.729%   $198.9432   $198.94   $198.95   $198.90  
  Purchase #3 $229.87   11.541%   $256.3993   $256.40   $256.40   $256.40  
  Purchase #4 $209.47   8.300%   $226.856   $226.86   $226.85   $226.90  
  Purchase #5 $42.83   6.848%   $45.763   $45.76   $45.75   $45.80  
  Purchase #6 $103.70   5.144%   $109.0343   $109.03   $109.05   $109.00  
  Purchase #7 $6.69   5.704%   $7.0716   $7.07   $7.05   $7.10  
  7 purchase totals = $812.16       $877.3033   $877.30   $877.30   $877.30