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	$160.96	7.158%	$172.4815	$172.48	$172.50	$172.50
Purchase #2	$227.90	12.442%	$256.2553	$256.26	$256.25	$256.30
Purchase #3	$67.75	11.770%	$75.7242	$75.72	$75.70	$75.70
Purchase #4	$189.27	9.614%	$207.4664	$207.47	$207.45	$207.50
Purchase #5	$122.35	5.300%	$128.8346	$128.83	$128.85	$128.80
Purchase #6	$234.89	3.845%	$243.9215	$243.92	$243.90	$243.90
Purchase #7	$145.69	4.658%	$152.4762	$152.48	$152.50	$152.50
7 purchase totals =	$1,148.81		$1,237.1597	$1,237.16	$1,237.15	$1,237.20