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	$178.44	6.725%	$190.4401	$190.44	$190.45	$190.40
Purchase #2	$54.36	3.138%	$56.0658	$56.07	$56.05	$56.10
Purchase #3	$67.91	10.220%	$74.8504	$74.85	$74.85	$74.90
Purchase #4	$18.53	9.453%	$20.2816	$20.28	$20.30	$20.30
Purchase #5	$125.52	9.476%	$137.4143	$137.41	$137.40	$137.40
Purchase #6	$54.49	8.340%	$59.0345	$59.03	$59.05	$59.00
Purchase #7	$55.25	10.501%	$61.0518	$61.05	$61.05	$61.10
7 purchase totals =	$554.50		$599.1385	$599.13	$599.15	$599.20