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	$106.79	4.729%	$111.8401	$111.84	$111.85	$111.80
Purchase #2	$226.87	11.556%	$253.0871	$253.09	$253.10	$253.10
Purchase #3	$219.86	7.575%	$236.5144	$236.51	$236.50	$236.50
Purchase #4	$70.68	7.764%	$76.1676	$76.17	$76.15	$76.20
Purchase #5	$75.59	6.468%	$80.4792	$80.48	$80.50	$80.50
Purchase #6	$186.60	10.106%	$205.4578	$205.46	$205.45	$205.50
Purchase #7	$53.97	5.423%	$56.8968	$56.90	$56.90	$56.90
7 purchase totals =	$940.36		$1,020.4430	$1,020.45	$1,020.45	$1,020.50