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	$201.71	10.279%	$222.4438	$222.44	$222.45	$222.40
Purchase #2	$111.94	5.524%	$118.1236	$118.12	$118.10	$118.10
Purchase #3	$33.47	11.600%	$37.3525	$37.35	$37.35	$37.40
Purchase #4	$122.45	7.430%	$131.548	$131.55	$131.55	$131.50
Purchase #5	$92.89	11.403%	$103.4822	$103.48	$103.50	$103.50
Purchase #6	$158.30	12.804%	$178.5687	$178.57	$178.55	$178.60
Purchase #7	$46.55	6.688%	$49.6633	$49.66	$49.65	$49.70
7 purchase totals =	$767.31		$841.1821	$841.17	$841.15	$841.20