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	$210.55	12.223%	$236.2855	$236.29	$236.30	$236.30
Purchase #2	$94.68	5.689%	$100.0663	$100.07	$100.05	$100.10
Purchase #3	$47.88	13.256%	$54.227	$54.23	$54.25	$54.20
Purchase #4	$211.60	5.476%	$223.1872	$223.19	$223.20	$223.20
Purchase #5	$162.26	6.524%	$172.8458	$172.85	$172.85	$172.80
Purchase #6	$67.76	4.485%	$70.799	$70.80	$70.80	$70.80
Purchase #7	$212.90	12.802%	$240.1555	$240.16	$240.15	$240.20
7 purchase totals =	$1,007.63		$1,097.5663	$1,097.59	$1,097.60	$1,097.60