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	$70.61	9.496%	$77.3151	$77.32	$77.30	$77.30
Purchase #2	$83.62	10.770%	$92.6259	$92.63	$92.65	$92.60
Purchase #3	$248.65	9.345%	$271.8863	$271.89	$271.90	$271.90
Purchase #4	$83.81	9.293%	$91.5985	$91.60	$91.60	$91.60
Purchase #5	$192.83	6.567%	$205.4931	$205.49	$205.50	$205.50
Purchase #6	$138.84	9.440%	$151.9465	$151.95	$151.95	$151.90
Purchase #7	$245.51	11.810%	$274.5047	$274.50	$274.50	$274.50
7 purchase totals =	$1,063.87		$1,165.3701	$1,165.38	$1,165.40	$1,165.30