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	$31.93	3.636%	$33.091	$33.09	$33.10	$33.10
Purchase #2	$204.47	9.193%	$223.2669	$223.27	$223.25	$223.30
Purchase #3	$19.66	13.498%	$22.3137	$22.31	$22.30	$22.30
Purchase #4	$19.46	10.317%	$21.4677	$21.47	$21.45	$21.50
Purchase #5	$83.33	11.131%	$92.6055	$92.61	$92.60	$92.60
Purchase #6	$127.65	7.742%	$137.5327	$137.53	$137.55	$137.50
Purchase #7	$105.51	9.760%	$115.8078	$115.81	$115.80	$115.80
7 purchase totals =	$592.01		$646.0853	$646.09	$646.05	$646.10