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 $121.69   9.310%   $133.0193   $133.02   $133.00   $133.00  
  Purchase #2 $155.38   6.149%   $164.9343   $164.93   $164.95   $164.90  
  Purchase #3 $250.94   7.417%   $269.5522   $269.55   $269.55   $269.60  
  Purchase #4 $48.82   13.866%   $55.5894   $55.59   $55.60   $55.60  
  Purchase #5 $92.81   4.520%   $97.005   $97.01   $97.00   $97.00  
  Purchase #6 $112.61   12.587%   $126.7842   $126.78   $126.80   $126.80  
  Purchase #7 $75.69   9.562%   $82.9275   $82.93   $82.95   $82.90  
  7 purchase totals = $857.94       $929.8119   $929.81   $929.85   $929.80