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	$93.56	12.641%	$105.3869	$105.39	$105.40	$105.40
Purchase #2	$220.37	4.855%	$231.069	$231.07	$231.05	$231.10
Purchase #3	$38.35	10.104%	$42.2249	$42.22	$42.20	$42.20
Purchase #4	$113.55	12.610%	$127.8687	$127.87	$127.85	$127.90
Purchase #5	$127.25	5.203%	$133.8708	$133.87	$133.85	$133.90
Purchase #6	$26.63	6.211%	$28.284	$28.28	$28.30	$28.30
Purchase #7	$82.93	8.418%	$89.911	$89.91	$89.90	$89.90
7 purchase totals =	$702.64		$758.6153	$758.61	$758.55	$758.70