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	$132.34	3.293%	$136.698	$136.70	$136.70	$136.70
Purchase #2	$98.32	11.439%	$109.5668	$109.57	$109.55	$109.60
Purchase #3	$164.90	11.720%	$184.2263	$184.23	$184.25	$184.20
Purchase #4	$105.63	11.764%	$118.0563	$118.06	$118.05	$118.10
Purchase #5	$50.49	5.424%	$53.2286	$53.23	$53.25	$53.20
Purchase #6	$244.39	7.573%	$262.8977	$262.90	$262.90	$262.90
Purchase #7	$95.33	9.618%	$104.4988	$104.50	$104.50	$104.50
7 purchase totals =	$891.40		$969.1725	$969.19	$969.20	$969.20