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	$77.69	13.422%	$88.1176	$88.12	$88.10	$88.10
Purchase #2	$236.53	4.751%	$247.7675	$247.77	$247.75	$247.80
Purchase #3	$129.91	8.637%	$141.1303	$141.13	$141.15	$141.10
Purchase #4	$51.58	3.831%	$53.556	$53.56	$53.55	$53.60
Purchase #5	$167.69	13.493%	$190.3164	$190.32	$190.30	$190.30
Purchase #6	$90.58	8.847%	$98.5936	$98.59	$98.60	$98.60
Purchase #7	$70.79	12.260%	$79.4689	$79.47	$79.45	$79.50
7 purchase totals =	$824.77		$898.9503	$898.96	$898.90	$899.00