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	$40.39	6.261%	$42.9188	$42.92	$42.90	$42.90
Purchase #2	$55.70	13.248%	$63.0791	$63.08	$63.10	$63.10
Purchase #3	$67.33	8.199%	$72.8504	$72.85	$72.85	$72.90
Purchase #4	$142.89	11.149%	$158.8208	$158.82	$158.80	$158.80
Purchase #5	$17.28	13.620%	$19.6335	$19.63	$19.65	$19.60
Purchase #6	$7.42	6.532%	$7.9047	$7.90	$7.90	$7.90
Purchase #7	$108.30	13.702%	$123.1393	$123.14	$123.15	$123.10
7 purchase totals =	$439.31		$488.3466	$488.34	$488.35	$488.30