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	$96.89	3.680%	$100.4556	$100.46	$100.45	$100.50
Purchase #2	$139.93	9.499%	$153.222	$153.22	$153.20	$153.20
Purchase #3	$150.54	6.853%	$160.8565	$160.86	$160.85	$160.90
Purchase #4	$245.48	12.404%	$275.9293	$275.93	$275.95	$275.90
Purchase #5	$132.35	10.117%	$145.7398	$145.74	$145.75	$145.70
Purchase #6	$234.79	9.322%	$256.6771	$256.68	$256.70	$256.70
Purchase #7	$91.41	12.203%	$102.5648	$102.56	$102.55	$102.60
7 purchase totals =	$1,091.39		$1,195.4451	$1,195.45	$1,195.45	$1,195.50