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	$150.51	13.801%	$171.2819	$171.28	$171.30	$171.30
Purchase #2	$56.49	7.212%	$60.5641	$60.56	$60.55	$60.60
Purchase #3	$110.54	13.576%	$125.5469	$125.55	$125.55	$125.50
Purchase #4	$241.51	4.294%	$251.8804	$251.88	$251.90	$251.90
Purchase #5	$176.67	4.238%	$184.1573	$184.16	$184.15	$184.20
Purchase #6	$184.96	10.363%	$204.1274	$204.13	$204.15	$204.10
Purchase #7	$158.91	10.294%	$175.2682	$175.27	$175.25	$175.30
7 purchase totals =	$1,079.59		$1,172.8262	$1,172.83	$1,172.85	$1,172.90