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	$5.60	12.791%	$6.3163	$6.32	$6.30	$6.30
Purchase #2	$243.70	7.360%	$261.6363	$261.64	$261.65	$261.60
Purchase #3	$201.68	10.155%	$222.1606	$222.16	$222.15	$222.20
Purchase #4	$47.85	11.281%	$53.248	$53.25	$53.25	$53.20
Purchase #5	$190.27	3.514%	$196.9561	$196.96	$196.95	$197.00
Purchase #6	$85.51	4.654%	$89.4896	$89.49	$89.50	$89.50
Purchase #7	$45.50	6.516%	$48.4648	$48.46	$48.45	$48.50
7 purchase totals =	$820.11		$878.2717	$878.28	$878.25	$878.30