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	$150.94	9.202%	$164.8295	$164.83	$164.85	$164.80
Purchase #2	$48.38	10.198%	$53.3138	$53.31	$53.30	$53.30
Purchase #3	$196.41	4.668%	$205.5784	$205.58	$205.60	$205.60
Purchase #4	$37.91	8.232%	$41.0308	$41.03	$41.05	$41.00
Purchase #5	$124.42	5.818%	$131.6588	$131.66	$131.65	$131.70
Purchase #6	$30.54	8.645%	$33.1802	$33.18	$33.20	$33.20
Purchase #7	$166.34	9.573%	$182.2637	$182.26	$182.25	$182.30
7 purchase totals =	$754.94		$811.8552	$811.85	$811.90	$811.90