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 $196.68   3.663%   $203.8844   $203.88   $203.90   $203.90  
  Purchase #2 $250.96   12.382%   $282.0339   $282.03   $282.05   $282.00  
  Purchase #3 $190.84   6.134%   $202.5461   $202.55   $202.55   $202.50  
  Purchase #4 $135.61   4.830%   $142.16   $142.16   $142.15   $142.20  
  Purchase #5 $206.73   5.345%   $217.7797   $217.78   $217.80   $217.80  
  Purchase #6 $54.59   8.782%   $59.3841   $59.38   $59.40   $59.40  
  Purchase #7 $55.50   6.193%   $58.9371   $58.94   $58.95   $58.90  
  7 purchase totals = $1,090.91       $1,166.7253   $1,166.72   $1,166.80   $1,166.70