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	$208.43	8.537%	$226.2237	$226.22	$226.20	$226.20
Purchase #2	$165.59	8.286%	$179.3108	$179.31	$179.30	$179.30
Purchase #3	$178.37	7.224%	$191.2554	$191.26	$191.25	$191.30
Purchase #4	$170.76	11.632%	$190.6228	$190.62	$190.60	$190.60
Purchase #5	$250.62	5.169%	$263.5745	$263.57	$263.55	$263.60
Purchase #6	$126.54	4.217%	$131.8762	$131.88	$131.90	$131.90
Purchase #7	$90.56	11.128%	$100.6375	$100.64	$100.65	$100.60
7 purchase totals =	$1,190.87		$1,283.5009	$1,283.50	$1,283.45	$1,283.50