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	$77.54	7.534%	$83.3819	$83.38	$83.40	$83.40
Purchase #2	$250.96	9.693%	$275.2856	$275.29	$275.30	$275.30
Purchase #3	$96.33	8.297%	$104.3225	$104.32	$104.30	$104.30
Purchase #4	$212.39	13.480%	$241.0202	$241.02	$241.00	$241.00
Purchase #5	$140.42	7.275%	$150.6356	$150.64	$150.65	$150.60
Purchase #6	$39.96	4.634%	$41.8117	$41.81	$41.80	$41.80
Purchase #7	$197.48	10.469%	$218.1542	$218.15	$218.15	$218.20
7 purchase totals =	$1,015.08		$1,114.6117	$1,114.61	$1,114.60	$1,114.60