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	$228.36	13.773%	$259.812	$259.81	$259.80	$259.80
Purchase #2	$36.59	11.278%	$40.7166	$40.72	$40.70	$40.70
Purchase #3	$127.59	7.685%	$137.3953	$137.40	$137.40	$137.40
Purchase #4	$200.78	12.417%	$225.7109	$225.71	$225.70	$225.70
Purchase #5	$18.62	12.107%	$20.8743	$20.87	$20.85	$20.90
Purchase #6	$79.67	12.727%	$89.8096	$89.81	$89.80	$89.80
Purchase #7	$72.59	10.129%	$79.9426	$79.94	$79.95	$79.90
7 purchase totals =	$764.20		$854.2613	$854.26	$854.20	$854.20