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 $250.25   5.572%   $264.1939   $264.19   $264.20   $264.20  
  Purchase #2 $17.56   10.201%   $19.3513   $19.35   $19.35   $19.40  
  Purchase #3 $204.42   5.465%   $215.5916   $215.59   $215.60   $215.60  
  Purchase #4 $231.43   5.862%   $244.9964   $245.00   $245.00   $245.00  
  Purchase #5 $171.54   4.129%   $178.6229   $178.62   $178.60   $178.60  
  Purchase #6 $58.40   3.261%   $60.3044   $60.30   $60.30   $60.30  
  Purchase #7 $28.91   4.720%   $30.2746   $30.27   $30.25   $30.30  
  7 purchase totals = $962.51       $1,013.3351   $1,013.32   $1,013.30   $1,013.40