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	$170.30	3.143%	$175.6525	$175.65	$175.65	$175.70
Purchase #2	$83.75	7.728%	$90.2222	$90.22	$90.20	$90.20
Purchase #3	$238.74	6.216%	$253.5801	$253.58	$253.60	$253.60
Purchase #4	$246.63	13.188%	$279.1556	$279.16	$279.15	$279.20
Purchase #5	$135.73	5.659%	$143.411	$143.41	$143.40	$143.40
Purchase #6	$94.65	7.249%	$101.5112	$101.51	$101.50	$101.50
Purchase #7	$33.50	11.463%	$37.3401	$37.34	$37.35	$37.30
7 purchase totals =	$1,003.30		$1,080.8727	$1,080.87	$1,080.85	$1,080.90