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	$171.72	9.247%	$187.5989	$187.60	$187.60	$187.60
Purchase #2	$80.44	3.390%	$83.1669	$83.17	$83.15	$83.20
Purchase #3	$152.28	4.861%	$159.6823	$159.68	$159.70	$159.70
Purchase #4	$79.76	7.747%	$85.939	$85.94	$85.95	$85.90
Purchase #5	$110.86	7.451%	$119.1202	$119.12	$119.10	$119.10
Purchase #6	$138.27	8.666%	$150.2525	$150.25	$150.25	$150.30
Purchase #7	$36.92	9.192%	$40.3137	$40.31	$40.30	$40.30
7 purchase totals =	$770.25		$826.0735	$826.07	$826.05	$826.10