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	$53.57	11.213%	$59.5768	$59.58	$59.60	$59.60
Purchase #2	$69.70	5.487%	$73.5244	$73.52	$73.50	$73.50
Purchase #3	$110.65	8.582%	$120.146	$120.15	$120.15	$120.10
Purchase #4	$181.42	5.191%	$190.8375	$190.84	$190.85	$190.80
Purchase #5	$54.67	13.242%	$61.9094	$61.91	$61.90	$61.90
Purchase #6	$48.57	7.515%	$52.22	$52.22	$52.20	$52.20
Purchase #7	$101.48	9.727%	$111.351	$111.35	$111.35	$111.40
7 purchase totals =	$620.06		$669.5651	$669.57	$669.55	$669.50