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	$122.42	13.369%	$138.7863	$138.79	$138.80	$138.80
Purchase #2	$63.94	12.524%	$71.9478	$71.95	$71.95	$71.90
Purchase #3	$99.94	3.375%	$103.313	$103.31	$103.30	$103.30
Purchase #4	$235.26	12.339%	$264.2887	$264.29	$264.30	$264.30
Purchase #5	$31.42	4.501%	$32.8342	$32.83	$32.85	$32.80
Purchase #6	$132.87	8.518%	$144.1879	$144.19	$144.20	$144.20
Purchase #7	$146.90	12.851%	$165.7781	$165.78	$165.80	$165.80
7 purchase totals =	$832.75		$921.1360	$921.14	$921.20	$921.10