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 $166.36   5.648%   $175.756   $175.76   $175.75   $175.80  
  Purchase #2 $22.95   3.134%   $23.6693   $23.67   $23.65   $23.70  
  Purchase #3 $76.89   8.679%   $83.5633   $83.56   $83.55   $83.60  
  Purchase #4 $51.33   11.673%   $57.3218   $57.32   $57.30   $57.30  
  Purchase #5 $250.66   7.427%   $269.2765   $269.28   $269.30   $269.30  
  Purchase #6 $214.72   9.676%   $235.4963   $235.50   $235.50   $235.50  
  Purchase #7 $109.55   7.702%   $117.9875   $117.99   $118.00   $118.00  
  7 purchase totals = $892.46       $963.0707   $963.08   $963.05   $963.20