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 $228.90   3.825%   $237.6554   $237.66   $237.65   $237.70  
  Purchase #2 $241.55   6.113%   $256.316   $256.32   $256.30   $256.30  
  Purchase #3 $31.59   6.348%   $33.5953   $33.60   $33.60   $33.60  
  Purchase #4 $23.91   9.719%   $26.2338   $26.23   $26.25   $26.20  
  Purchase #5 $88.83   7.413%   $95.415   $95.42   $95.40   $95.40  
  Purchase #6 $61.83   12.819%   $69.756   $69.76   $69.75   $69.80  
  Purchase #7 $117.79   6.116%   $124.994   $124.99   $125.00   $125.00  
  7 purchase totals = $794.40       $843.9655   $843.98   $843.95   $844.00