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 $155.59   12.559%   $175.1305   $175.13   $175.15   $175.10  
  Purchase #2 $53.78   11.160%   $59.7818   $59.78   $59.80   $59.80  
  Purchase #3 $21.78   3.260%   $22.49   $22.49   $22.50   $22.50  
  Purchase #4 $24.82   8.487%   $26.9265   $26.93   $26.95   $26.90  
  Purchase #5 $94.44   8.569%   $102.5326   $102.53   $102.55   $102.50  
  Purchase #6 $249.60   5.773%   $264.0094   $264.01   $264.00   $264.00  
  Purchase #7 $164.38   11.328%   $183.001   $183.00   $183.00   $183.00  
  7 purchase totals = $764.39       $833.8718   $833.87   $833.95   $833.80