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	$33.96	3.561%	$35.1693	$35.17	$35.15	$35.20
Purchase #2	$103.85	4.522%	$108.5461	$108.55	$108.55	$108.50
Purchase #3	$244.43	8.202%	$264.4781	$264.48	$264.50	$264.50
Purchase #4	$81.47	10.712%	$90.1971	$90.20	$90.20	$90.20
Purchase #5	$73.99	11.572%	$82.5521	$82.55	$82.55	$82.60
Purchase #6	$135.58	13.209%	$153.4888	$153.49	$153.50	$153.50
Purchase #7	$152.83	12.820%	$172.4228	$172.42	$172.40	$172.40
7 purchase totals =	$826.11		$906.8543	$906.86	$906.85	$906.90