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	$152.29	12.833%	$171.8334	$171.83	$171.85	$171.80
Purchase #2	$230.49	3.491%	$238.5364	$238.54	$238.55	$238.50
Purchase #3	$154.88	6.652%	$165.1826	$165.18	$165.20	$165.20
Purchase #4	$9.46	6.844%	$10.1074	$10.11	$10.10	$10.10
Purchase #5	$161.66	11.427%	$180.1329	$180.13	$180.15	$180.10
Purchase #6	$69.32	12.530%	$78.0058	$78.01	$78.00	$78.00
Purchase #7	$135.82	5.601%	$143.4273	$143.43	$143.45	$143.40
7 purchase totals =	$913.92		$987.2258	$987.23	$987.30	$987.10