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	$73.54	6.253%	$78.1385	$78.14	$78.15	$78.10
Purchase #2	$99.67	4.778%	$104.4322	$104.43	$104.45	$104.40
Purchase #3	$144.52	12.729%	$162.916	$162.92	$162.90	$162.90
Purchase #4	$180.89	8.514%	$196.291	$196.29	$196.30	$196.30
Purchase #5	$87.95	13.130%	$99.4978	$99.50	$99.50	$99.50
Purchase #6	$60.40	10.367%	$66.6617	$66.66	$66.65	$66.70
Purchase #7	$133.49	6.502%	$142.1695	$142.17	$142.15	$142.20
7 purchase totals =	$780.46		$850.1067	$850.11	$850.10	$850.10