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	$129.53	7.831%	$139.6735	$139.67	$139.65	$139.70
Purchase #2	$120.44	6.715%	$128.5275	$128.53	$128.55	$128.50
Purchase #3	$70.92	9.279%	$77.5007	$77.50	$77.50	$77.50
Purchase #4	$156.52	5.748%	$165.5168	$165.52	$165.50	$165.50
Purchase #5	$50.72	8.817%	$55.192	$55.19	$55.20	$55.20
Purchase #6	$72.51	13.291%	$82.1473	$82.15	$82.15	$82.10
Purchase #7	$15.60	9.427%	$17.0706	$17.07	$17.05	$17.10
7 purchase totals =	$616.24		$665.6284	$665.63	$665.60	$665.60