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	$245.59	4.292%	$256.1307	$256.13	$256.15	$256.10
Purchase #2	$185.29	10.360%	$204.486	$204.49	$204.50	$204.50
Purchase #3	$247.51	10.417%	$273.2931	$273.29	$273.30	$273.30
Purchase #4	$89.79	7.482%	$96.5081	$96.51	$96.50	$96.50
Purchase #5	$165.42	12.341%	$185.8345	$185.83	$185.85	$185.80
Purchase #6	$58.48	5.657%	$61.7882	$61.79	$61.80	$61.80
Purchase #7	$157.64	11.149%	$175.2153	$175.22	$175.20	$175.20
7 purchase totals =	$1,149.72		$1,253.2559	$1,253.26	$1,253.30	$1,253.20