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	$178.62	12.247%	$200.4956	$200.50	$200.50	$200.50
Purchase #2	$50.54	7.251%	$54.2047	$54.20	$54.20	$54.20
Purchase #3	$106.69	4.483%	$111.4729	$111.47	$111.45	$111.50
Purchase #4	$38.91	3.579%	$40.3026	$40.30	$40.30	$40.30
Purchase #5	$6.43	12.548%	$7.2368	$7.24	$7.25	$7.20
Purchase #6	$29.29	11.193%	$32.5684	$32.57	$32.55	$32.60
Purchase #7	$196.46	6.789%	$209.7977	$209.80	$209.80	$209.80
7 purchase totals =	$606.94		$656.0787	$656.08	$656.05	$656.10