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	$250.86	11.435%	$279.5458	$279.55	$279.55	$279.50
Purchase #2	$83.65	7.601%	$90.0082	$90.01	$90.00	$90.00
Purchase #3	$56.57	11.461%	$63.0535	$63.05	$63.05	$63.10
Purchase #4	$229.93	5.861%	$243.4062	$243.41	$243.40	$243.40
Purchase #5	$106.81	13.235%	$120.9463	$120.95	$120.95	$120.90
Purchase #6	$68.96	13.261%	$78.1048	$78.10	$78.10	$78.10
Purchase #7	$172.43	9.162%	$188.228	$188.23	$188.25	$188.20
7 purchase totals =	$969.21		$1,063.2928	$1,063.30	$1,063.30	$1,063.20