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	$139.77	13.804%	$159.0639	$159.06	$159.05	$159.10
Purchase #2	$168.94	7.473%	$181.5649	$181.56	$181.55	$181.60
Purchase #3	$172.61	11.404%	$192.2944	$192.29	$192.30	$192.30
Purchase #4	$165.54	9.500%	$181.2663	$181.27	$181.25	$181.30
Purchase #5	$10.87	3.359%	$11.2351	$11.24	$11.25	$11.20
Purchase #6	$96.74	7.384%	$103.8833	$103.88	$103.90	$103.90
Purchase #7	$136.46	5.417%	$143.852	$143.85	$143.85	$143.90
7 purchase totals =	$890.93		$973.1599	$973.15	$973.15	$973.30