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	$80.28	12.709%	$90.4828	$90.48	$90.50	$90.50
Purchase #2	$238.41	3.322%	$246.33	$246.33	$246.35	$246.30
Purchase #3	$192.29	10.294%	$212.0843	$212.08	$212.10	$212.10
Purchase #4	$124.96	9.753%	$137.1473	$137.15	$137.15	$137.10
Purchase #5	$242.65	5.722%	$256.5344	$256.53	$256.55	$256.50
Purchase #6	$223.52	11.662%	$249.5869	$249.59	$249.60	$249.60
Purchase #7	$158.50	11.240%	$176.3154	$176.32	$176.30	$176.30
7 purchase totals =	$1,260.61		$1,368.4811	$1,368.48	$1,368.55	$1,368.40