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	$26.27	8.324%	$28.4567	$28.46	$28.45	$28.50
Purchase #2	$12.63	13.783%	$14.3708	$14.37	$14.35	$14.40
Purchase #3	$185.57	7.144%	$198.8271	$198.83	$198.85	$198.80
Purchase #4	$131.32	12.290%	$147.4592	$147.46	$147.45	$147.50
Purchase #5	$44.47	13.263%	$50.3681	$50.37	$50.35	$50.40
Purchase #6	$89.46	13.140%	$101.215	$101.22	$101.20	$101.20
Purchase #7	$150.71	6.249%	$160.1279	$160.13	$160.15	$160.10
7 purchase totals =	$640.43		$700.8248	$700.84	$700.80	$700.90