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	$97.91	11.700%	$109.3655	$109.37	$109.35	$109.40
Purchase #2	$151.61	13.766%	$172.4806	$172.48	$172.50	$172.50
Purchase #3	$116.41	4.245%	$121.3516	$121.35	$121.35	$121.40
Purchase #4	$85.36	7.168%	$91.4786	$91.48	$91.50	$91.50
Purchase #5	$166.63	7.546%	$179.2039	$179.20	$179.20	$179.20
Purchase #6	$121.34	5.375%	$127.862	$127.86	$127.85	$127.90
Purchase #7	$36.56	4.602%	$38.2425	$38.24	$38.25	$38.20
7 purchase totals =	$775.82		$839.9847	$839.98	$840.00	$840.10