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	$120.34	6.414%	$128.0586	$128.06	$128.05	$128.10
Purchase #2	$36.47	8.395%	$39.5317	$39.53	$39.55	$39.50
Purchase #3	$82.26	11.730%	$91.9091	$91.91	$91.90	$91.90
Purchase #4	$118.51	4.751%	$124.1404	$124.14	$124.15	$124.10
Purchase #5	$17.87	13.834%	$20.3421	$20.34	$20.35	$20.30
Purchase #6	$200.68	5.718%	$212.1549	$212.15	$212.15	$212.20
Purchase #7	$250.46	12.797%	$282.5114	$282.51	$282.50	$282.50
7 purchase totals =	$826.59		$898.6482	$898.64	$898.65	$898.60