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	$151.75	9.815%	$166.6443	$166.64	$166.65	$166.60
Purchase #2	$24.49	12.509%	$27.5535	$27.55	$27.55	$27.60
Purchase #3	$208.80	3.617%	$216.3523	$216.35	$216.35	$216.40
Purchase #4	$124.61	7.118%	$133.4797	$133.48	$133.50	$133.50
Purchase #5	$10.34	4.557%	$10.8112	$10.81	$10.80	$10.80
Purchase #6	$75.54	13.463%	$85.71	$85.71	$85.70	$85.70
Purchase #7	$187.33	4.757%	$196.2413	$196.24	$196.25	$196.20
7 purchase totals =	$782.86		$836.7923	$836.78	$836.80	$836.80