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	$35.80	7.544%	$38.5008	$38.50	$38.50	$38.50
Purchase #2	$25.78	5.322%	$27.152	$27.15	$27.15	$27.20
Purchase #3	$131.40	11.762%	$146.8553	$146.86	$146.85	$146.90
Purchase #4	$81.40	4.784%	$85.2942	$85.29	$85.30	$85.30
Purchase #5	$28.68	13.146%	$32.4503	$32.45	$32.45	$32.50
Purchase #6	$69.39	6.265%	$73.7373	$73.74	$73.75	$73.70
Purchase #7	$41.84	6.528%	$44.5713	$44.57	$44.55	$44.60
7 purchase totals =	$414.29		$448.5612	$448.56	$448.55	$448.70