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	$143.86	7.467%	$154.602	$154.60	$154.60	$154.60
Purchase #2	$96.64	9.368%	$105.6932	$105.69	$105.70	$105.70
Purchase #3	$17.71	13.157%	$20.0401	$20.04	$20.05	$20.00
Purchase #4	$250.71	5.167%	$263.6642	$263.66	$263.65	$263.70
Purchase #5	$75.85	12.764%	$85.5315	$85.53	$85.55	$85.50
Purchase #6	$87.52	12.499%	$98.4591	$98.46	$98.45	$98.50
Purchase #7	$226.91	8.181%	$245.4735	$245.47	$245.45	$245.50
7 purchase totals =	$899.20		$973.4636	$973.45	$973.45	$973.50