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 $147.95   3.541%   $153.1889   $153.19   $153.20   $153.20  
  Purchase #2 $13.53   7.120%   $14.4933   $14.49   $14.50   $14.50  
  Purchase #3 $183.85   7.778%   $198.1499   $198.15   $198.15   $198.10  
  Purchase #4 $115.61   8.539%   $125.4819   $125.48   $125.50   $125.50  
  Purchase #5 $94.90   10.490%   $104.855   $104.86   $104.85   $104.90  
  Purchase #6 $85.93   5.192%   $90.3915   $90.39   $90.40   $90.40  
  Purchase #7 $231.38   8.403%   $250.8229   $250.82   $250.80   $250.80  
  7 purchase totals = $873.15       $937.3834   $937.38   $937.40   $937.40