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	$249.29	12.868%	$281.3686	$281.37	$281.35	$281.40
Purchase #2	$36.38	10.824%	$40.3178	$40.32	$40.30	$40.30
Purchase #3	$57.72	8.734%	$62.7613	$62.76	$62.75	$62.80
Purchase #4	$73.78	13.569%	$83.7912	$83.79	$83.80	$83.80
Purchase #5	$188.86	13.475%	$214.3089	$214.31	$214.30	$214.30
Purchase #6	$124.72	3.289%	$128.822	$128.82	$128.80	$128.80
Purchase #7	$59.27	6.555%	$63.1551	$63.16	$63.15	$63.20
7 purchase totals =	$790.02		$874.5249	$874.53	$874.45	$874.60