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	$235.85	8.552%	$256.0199	$256.02	$256.00	$256.00
Purchase #2	$93.63	13.123%	$105.9171	$105.92	$105.90	$105.90
Purchase #3	$148.85	8.515%	$161.5246	$161.52	$161.50	$161.50
Purchase #4	$202.67	11.241%	$225.4521	$225.45	$225.45	$225.50
Purchase #5	$151.54	6.131%	$160.8309	$160.83	$160.85	$160.80
Purchase #6	$64.54	4.215%	$67.2604	$67.26	$67.25	$67.30
Purchase #7	$107.88	11.372%	$120.1481	$120.15	$120.15	$120.10
7 purchase totals =	$1,004.96		$1,097.1531	$1,097.15	$1,097.10	$1,097.10