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 $94.73   10.579%   $104.7515   $104.75   $104.75   $104.80  
  Purchase #2 $157.77   10.625%   $174.5331   $174.53   $174.55   $174.50  
  Purchase #3 $177.89   11.866%   $198.9984   $199.00   $199.00   $199.00  
  Purchase #4 $202.34   13.203%   $229.055   $229.06   $229.05   $229.10  
  Purchase #5 $98.84   11.211%   $109.921   $109.92   $109.90   $109.90  
  Purchase #6 $222.83   9.663%   $244.3621   $244.36   $244.35   $244.40  
  Purchase #7 $171.87   7.262%   $184.3512   $184.35   $184.35   $184.40  
  7 purchase totals = $1,126.27       $1,245.9723   $1,245.97   $1,245.95   $1,246.10