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	$11.75	4.130%	$12.2353	$12.24	$12.25	$12.20
Purchase #2	$55.47	7.873%	$59.8372	$59.84	$59.85	$59.80
Purchase #3	$102.64	11.595%	$114.5411	$114.54	$114.55	$114.50
Purchase #4	$100.43	6.469%	$106.9268	$106.93	$106.95	$106.90
Purchase #5	$89.48	12.446%	$100.6167	$100.62	$100.60	$100.60
Purchase #6	$244.49	6.234%	$259.7315	$259.73	$259.75	$259.70
Purchase #7	$209.65	13.151%	$237.2211	$237.22	$237.20	$237.20
7 purchase totals =	$813.91		$891.1097	$891.12	$891.15	$890.90