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	$248.43	12.662%	$279.8862	$279.89	$279.90	$279.90
Purchase #2	$186.33	7.453%	$200.2172	$200.22	$200.20	$200.20
Purchase #3	$184.52	6.713%	$196.9068	$196.91	$196.90	$196.90
Purchase #4	$235.73	8.625%	$256.0617	$256.06	$256.05	$256.10
Purchase #5	$159.75	7.284%	$171.3862	$171.39	$171.40	$171.40
Purchase #6	$88.65	8.348%	$96.0505	$96.05	$96.05	$96.10
Purchase #7	$49.26	7.425%	$52.9176	$52.92	$52.90	$52.90
7 purchase totals =	$1,152.67		$1,253.4262	$1,253.44	$1,253.40	$1,253.50