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	$153.49	4.240%	$159.998	$160.00	$160.00	$160.00
Purchase #2	$33.27	5.321%	$35.0403	$35.04	$35.05	$35.00
Purchase #3	$81.61	10.853%	$90.4671	$90.47	$90.45	$90.50
Purchase #4	$55.34	10.507%	$61.1546	$61.15	$61.15	$61.20
Purchase #5	$106.92	10.830%	$118.4994	$118.50	$118.50	$118.50
Purchase #6	$58.59	3.333%	$60.5428	$60.54	$60.55	$60.50
Purchase #7	$30.44	8.868%	$33.1394	$33.14	$33.15	$33.10
7 purchase totals =	$519.66		$558.8416	$558.84	$558.85	$558.80