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	$29.41	13.446%	$33.3645	$33.36	$33.35	$33.40
Purchase #2	$89.61	10.325%	$98.8622	$98.86	$98.85	$98.90
Purchase #3	$72.84	8.305%	$78.8894	$78.89	$78.90	$78.90
Purchase #4	$57.50	13.697%	$65.3758	$65.38	$65.40	$65.40
Purchase #5	$57.37	3.163%	$59.1846	$59.18	$59.20	$59.20
Purchase #6	$71.75	10.353%	$79.1783	$79.18	$79.20	$79.20
Purchase #7	$228.40	11.232%	$254.0539	$254.05	$254.05	$254.10
7 purchase totals =	$606.88		$668.9087	$668.90	$668.95	$669.10