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	$9.89	3.192%	$10.2057	$10.21	$10.20	$10.20
Purchase #2	$100.89	3.867%	$104.7914	$104.79	$104.80	$104.80
Purchase #3	$107.27	9.353%	$117.303	$117.30	$117.30	$117.30
Purchase #4	$105.31	11.540%	$117.4628	$117.46	$117.45	$117.50
Purchase #5	$41.26	11.304%	$45.924	$45.92	$45.90	$45.90
Purchase #6	$195.92	13.490%	$222.3496	$222.35	$222.35	$222.30
Purchase #7	$78.29	8.869%	$85.2335	$85.23	$85.25	$85.20
7 purchase totals =	$638.83		$703.2700	$703.26	$703.25	$703.20