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	$56.46	6.844%	$60.3241	$60.32	$60.30	$60.30
Purchase #2	$139.44	11.849%	$155.9622	$155.96	$155.95	$156.00
Purchase #3	$122.25	6.865%	$130.6425	$130.64	$130.65	$130.60
Purchase #4	$173.37	3.535%	$179.4986	$179.50	$179.50	$179.50
Purchase #5	$150.37	12.842%	$169.6805	$169.68	$169.70	$169.70
Purchase #6	$123.90	5.144%	$130.2734	$130.27	$130.25	$130.30
Purchase #7	$59.93	3.323%	$61.9215	$61.92	$61.90	$61.90
7 purchase totals =	$825.72		$888.3028	$888.29	$888.25	$888.30