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	$225.27	11.589%	$251.3765	$251.38	$251.40	$251.40
Purchase #2	$37.93	4.235%	$39.5363	$39.54	$39.55	$39.50
Purchase #3	$122.97	13.718%	$139.839	$139.84	$139.85	$139.80
Purchase #4	$123.93	3.226%	$127.928	$127.93	$127.95	$127.90
Purchase #5	$149.89	4.272%	$156.2933	$156.29	$156.30	$156.30
Purchase #6	$32.25	13.795%	$36.6989	$36.70	$36.70	$36.70
Purchase #7	$105.38	13.755%	$119.875	$119.88	$119.90	$119.90
7 purchase totals =	$797.62		$871.5470	$871.56	$871.65	$871.50