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	$71.37	9.667%	$78.2693	$78.27	$78.25	$78.30
Purchase #2	$85.60	11.652%	$95.5741	$95.57	$95.55	$95.60
Purchase #3	$243.53	5.317%	$256.4785	$256.48	$256.50	$256.50
Purchase #4	$244.44	11.403%	$272.3135	$272.31	$272.30	$272.30
Purchase #5	$159.31	7.457%	$171.1897	$171.19	$171.20	$171.20
Purchase #6	$242.40	3.642%	$251.2282	$251.23	$251.25	$251.20
Purchase #7	$127.50	8.558%	$138.4115	$138.41	$138.40	$138.40
7 purchase totals =	$1,174.15		$1,263.4648	$1,263.46	$1,263.45	$1,263.50