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	$54.92	12.635%	$61.8591	$61.86	$61.85	$61.90
Purchase #2	$143.26	5.132%	$150.6121	$150.61	$150.60	$150.60
Purchase #3	$236.93	5.480%	$249.9138	$249.91	$249.90	$249.90
Purchase #4	$210.54	6.478%	$224.1788	$224.18	$224.20	$224.20
Purchase #5	$164.90	13.560%	$187.2604	$187.26	$187.25	$187.30
Purchase #6	$5.72	8.589%	$6.2113	$6.21	$6.20	$6.20
Purchase #7	$85.40	4.250%	$89.0295	$89.03	$89.05	$89.00
7 purchase totals =	$901.67		$969.0650	$969.06	$969.05	$969.10