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	$39.81	9.170%	$43.4606	$43.46	$43.45	$43.50
Purchase #2	$6.50	13.741%	$7.3932	$7.39	$7.40	$7.40
Purchase #3	$126.91	7.399%	$136.3001	$136.30	$136.30	$136.30
Purchase #4	$200.78	4.535%	$209.8854	$209.89	$209.90	$209.90
Purchase #5	$75.68	12.378%	$85.0477	$85.05	$85.05	$85.00
Purchase #6	$25.68	12.376%	$28.8582	$28.86	$28.85	$28.90
Purchase #7	$116.71	8.710%	$126.8754	$126.88	$126.90	$126.90
7 purchase totals =	$592.07		$637.8206	$637.83	$637.85	$637.90