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	$64.77	9.728%	$71.0708	$71.07	$71.05	$71.10
Purchase #2	$57.60	5.754%	$60.9143	$60.91	$60.90	$60.90
Purchase #3	$95.89	3.839%	$99.5712	$99.57	$99.55	$99.60
Purchase #4	$158.79	4.871%	$166.5247	$166.52	$166.50	$166.50
Purchase #5	$130.89	10.277%	$144.3416	$144.34	$144.35	$144.30
Purchase #6	$71.39	7.428%	$76.6928	$76.69	$76.70	$76.70
Purchase #7	$48.89	3.261%	$50.4843	$50.48	$50.50	$50.50
7 purchase totals =	$628.22		$669.5997	$669.58	$669.55	$669.60