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	$30.44	9.340%	$33.2831	$33.28	$33.30	$33.30
Purchase #2	$55.78	10.307%	$61.5292	$61.53	$61.55	$61.50
Purchase #3	$147.62	12.717%	$166.3928	$166.39	$166.40	$166.40
Purchase #4	$56.67	9.190%	$61.878	$61.88	$61.90	$61.90
Purchase #5	$81.58	11.130%	$90.6599	$90.66	$90.65	$90.70
Purchase #6	$122.95	5.770%	$130.0442	$130.04	$130.05	$130.00
Purchase #7	$67.56	6.675%	$72.0696	$72.07	$72.05	$72.10
7 purchase totals =	$562.60		$615.8568	$615.85	$615.90	$615.90