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	$154.71	11.392%	$172.3346	$172.33	$172.35	$172.30
Purchase #2	$200.48	10.204%	$220.937	$220.94	$220.95	$220.90
Purchase #3	$80.33	9.577%	$88.0232	$88.02	$88.00	$88.00
Purchase #4	$99.44	6.325%	$105.7296	$105.73	$105.75	$105.70
Purchase #5	$76.41	9.249%	$83.4772	$83.48	$83.50	$83.50
Purchase #6	$226.83	3.840%	$235.5403	$235.54	$235.55	$235.50
Purchase #7	$89.94	8.277%	$97.3843	$97.38	$97.40	$97.40
7 purchase totals =	$928.14		$1,003.4262	$1,003.42	$1,003.50	$1,003.30