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	$150.70	5.164%	$158.4821	$158.48	$158.50	$158.50
Purchase #2	$98.52	7.233%	$105.646	$105.65	$105.65	$105.60
Purchase #3	$167.87	10.633%	$185.7196	$185.72	$185.70	$185.70
Purchase #4	$198.59	12.589%	$223.5905	$223.59	$223.60	$223.60
Purchase #5	$46.58	7.459%	$50.0544	$50.05	$50.05	$50.10
Purchase #6	$168.28	12.258%	$188.9078	$188.91	$188.90	$188.90
Purchase #7	$249.40	13.831%	$283.8945	$283.89	$283.90	$283.90
7 purchase totals =	$1,079.94		$1,196.2949	$1,196.29	$1,196.30	$1,196.30