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	$15.44	7.523%	$16.6016	$16.60	$16.60	$16.60
Purchase #2	$11.32	6.812%	$12.0911	$12.09	$12.10	$12.10
Purchase #3	$64.59	10.828%	$71.5838	$71.58	$71.60	$71.60
Purchase #4	$69.30	8.408%	$75.1267	$75.13	$75.15	$75.10
Purchase #5	$64.86	4.665%	$67.8857	$67.89	$67.90	$67.90
Purchase #6	$89.83	9.799%	$98.6324	$98.63	$98.65	$98.60
Purchase #7	$129.87	5.192%	$136.6129	$136.61	$136.60	$136.60
7 purchase totals =	$445.21		$478.5342	$478.53	$478.60	$478.50