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	$67.26	10.348%	$74.2201	$74.22	$74.20	$74.20
Purchase #2	$176.72	8.233%	$191.2694	$191.27	$191.25	$191.30
Purchase #3	$173.86	7.803%	$187.4263	$187.43	$187.45	$187.40
Purchase #4	$50.44	9.746%	$55.3559	$55.36	$55.35	$55.40
Purchase #5	$178.63	10.164%	$196.786	$196.79	$196.80	$196.80
Purchase #6	$43.91	4.479%	$45.8767	$45.88	$45.90	$45.90
Purchase #7	$204.74	13.175%	$231.7145	$231.71	$231.70	$231.70
7 purchase totals =	$895.56		$982.6489	$982.66	$982.65	$982.70