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	$79.93	12.501%	$89.922	$89.92	$89.90	$89.90
Purchase #2	$81.35	7.308%	$87.2951	$87.30	$87.30	$87.30
Purchase #3	$182.40	6.739%	$194.6919	$194.69	$194.70	$194.70
Purchase #4	$228.65	6.742%	$244.0656	$244.07	$244.05	$244.10
Purchase #5	$137.25	11.873%	$153.5457	$153.55	$153.55	$153.50
Purchase #6	$230.95	12.282%	$259.3153	$259.32	$259.30	$259.30
Purchase #7	$55.34	10.435%	$61.1147	$61.11	$61.10	$61.10
7 purchase totals =	$995.87		$1,089.9503	$1,089.96	$1,089.90	$1,089.90