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	$107.98	13.707%	$122.7808	$122.78	$122.80	$122.80
Purchase #2	$215.27	8.654%	$233.8995	$233.90	$233.90	$233.90
Purchase #3	$184.25	9.121%	$201.0554	$201.06	$201.05	$201.10
Purchase #4	$115.80	13.575%	$131.5199	$131.52	$131.50	$131.50
Purchase #5	$33.48	13.131%	$37.8763	$37.88	$37.90	$37.90
Purchase #6	$230.48	10.705%	$255.1529	$255.15	$255.15	$255.20
Purchase #7	$30.60	9.637%	$33.5489	$33.55	$33.55	$33.50
7 purchase totals =	$917.86		$1,015.8337	$1,015.84	$1,015.85	$1,015.90