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	$159.60	4.830%	$167.3087	$167.31	$167.30	$167.30
Purchase #2	$230.34	12.622%	$259.4135	$259.41	$259.40	$259.40
Purchase #3	$70.63	11.505%	$78.756	$78.76	$78.75	$78.80
Purchase #4	$76.72	9.153%	$83.7422	$83.74	$83.75	$83.70
Purchase #5	$226.89	9.507%	$248.4604	$248.46	$248.45	$248.50
Purchase #6	$56.77	11.551%	$63.3275	$63.33	$63.35	$63.30
Purchase #7	$87.92	3.363%	$90.8767	$90.88	$90.90	$90.90
7 purchase totals =	$908.87		$991.8850	$991.89	$991.90	$991.90