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	$108.47	11.591%	$121.0428	$121.04	$121.05	$121.00
Purchase #2	$212.36	8.806%	$231.0604	$231.06	$231.05	$231.10
Purchase #3	$124.84	10.279%	$137.6723	$137.67	$137.65	$137.70
Purchase #4	$162.67	7.252%	$174.4668	$174.47	$174.45	$174.50
Purchase #5	$112.52	9.751%	$123.4918	$123.49	$123.50	$123.50
Purchase #6	$53.92	10.679%	$59.6781	$59.68	$59.70	$59.70
Purchase #7	$152.74	5.103%	$160.5343	$160.53	$160.55	$160.50
7 purchase totals =	$927.52		$1,007.9465	$1,007.94	$1,007.95	$1,008.00