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	$109.94	12.415%	$123.5891	$123.59	$123.60	$123.60
Purchase #2	$16.51	6.503%	$17.5836	$17.58	$17.60	$17.60
Purchase #3	$235.67	11.367%	$262.4586	$262.46	$262.45	$262.50
Purchase #4	$69.34	4.425%	$72.4083	$72.41	$72.40	$72.40
Purchase #5	$35.80	3.732%	$37.1361	$37.14	$37.15	$37.10
Purchase #6	$11.85	7.123%	$12.6941	$12.69	$12.70	$12.70
Purchase #7	$200.71	12.412%	$225.6221	$225.62	$225.60	$225.60
7 purchase totals =	$679.82		$751.4919	$751.49	$751.50	$751.50