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	$156.84	5.402%	$165.3125	$165.31	$165.30	$165.30
Purchase #2	$209.87	10.312%	$231.5118	$231.51	$231.50	$231.50
Purchase #3	$66.83	4.463%	$69.8126	$69.81	$69.80	$69.80
Purchase #4	$24.26	4.213%	$25.2821	$25.28	$25.30	$25.30
Purchase #5	$176.78	12.234%	$198.4073	$198.41	$198.40	$198.40
Purchase #6	$132.53	5.327%	$139.5899	$139.59	$139.60	$139.60
Purchase #7	$249.50	8.491%	$270.685	$270.69	$270.70	$270.70
7 purchase totals =	$1,016.61		$1,100.6012	$1,100.60	$1,100.60	$1,100.60