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	$85.27	10.111%	$93.8916	$93.89	$93.90	$93.90
Purchase #2	$155.44	6.513%	$165.5638	$165.56	$165.55	$165.60
Purchase #3	$171.89	4.757%	$180.0668	$180.07	$180.05	$180.10
Purchase #4	$17.83	12.457%	$20.0511	$20.05	$20.05	$20.10
Purchase #5	$37.97	9.337%	$41.5153	$41.52	$41.50	$41.50
Purchase #6	$111.27	6.617%	$118.6327	$118.63	$118.65	$118.60
Purchase #7	$161.51	8.308%	$174.9283	$174.93	$174.95	$174.90
7 purchase totals =	$741.18		$794.6496	$794.65	$794.65	$794.70