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	$232.88	11.517%	$259.7008	$259.70	$259.70	$259.70
Purchase #2	$39.57	4.834%	$41.4828	$41.48	$41.50	$41.50
Purchase #3	$27.33	6.191%	$29.022	$29.02	$29.00	$29.00
Purchase #4	$90.80	10.470%	$100.3068	$100.31	$100.30	$100.30
Purchase #5	$145.92	6.560%	$155.4924	$155.49	$155.50	$155.50
Purchase #6	$214.66	12.119%	$240.6746	$240.67	$240.65	$240.70
Purchase #7	$30.31	10.501%	$33.4929	$33.49	$33.50	$33.50
7 purchase totals =	$781.47		$860.1723	$860.16	$860.15	$860.20