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	$250.80	7.144%	$268.7172	$268.72	$268.70	$268.70
Purchase #2	$165.61	5.375%	$174.5115	$174.51	$174.50	$174.50
Purchase #3	$135.33	8.322%	$146.5922	$146.59	$146.60	$146.60
Purchase #4	$143.72	9.321%	$157.1161	$157.12	$157.10	$157.10
Purchase #5	$123.45	3.117%	$127.2979	$127.30	$127.30	$127.30
Purchase #6	$37.76	12.414%	$42.4475	$42.45	$42.45	$42.40
Purchase #7	$137.33	12.533%	$154.5416	$154.54	$154.55	$154.50
7 purchase totals =	$994.00		$1,071.2240	$1,071.23	$1,071.20	$1,071.10