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	$37.28	13.677%	$42.3788	$42.38	$42.40	$42.40
Purchase #2	$249.35	6.310%	$265.084	$265.08	$265.10	$265.10
Purchase #3	$167.27	12.638%	$188.4096	$188.41	$188.40	$188.40
Purchase #4	$29.90	13.302%	$33.8773	$33.88	$33.90	$33.90
Purchase #5	$147.72	12.843%	$166.6917	$166.69	$166.70	$166.70
Purchase #6	$222.34	3.819%	$230.8312	$230.83	$230.85	$230.80
Purchase #7	$46.92	11.244%	$52.1957	$52.20	$52.20	$52.20
7 purchase totals =	$900.78		$979.4683	$979.47	$979.55	$979.50