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	$109.29	6.171%	$116.0343	$116.03	$116.05	$116.00
Purchase #2	$135.47	13.240%	$153.4062	$153.41	$153.40	$153.40
Purchase #3	$52.62	12.131%	$59.0033	$59.00	$59.00	$59.00
Purchase #4	$100.69	7.130%	$107.8692	$107.87	$107.85	$107.90
Purchase #5	$30.80	7.302%	$33.049	$33.05	$33.05	$33.00
Purchase #6	$151.49	4.797%	$158.757	$158.76	$158.75	$158.80
Purchase #7	$78.91	8.238%	$85.4106	$85.41	$85.40	$85.40
7 purchase totals =	$659.27		$713.5296	$713.53	$713.50	$713.50