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	$78.89	4.108%	$82.1308	$82.13	$82.15	$82.10
Purchase #2	$175.38	5.342%	$184.7488	$184.75	$184.75	$184.70
Purchase #3	$225.31	13.168%	$254.9788	$254.98	$255.00	$255.00
Purchase #4	$154.35	4.196%	$160.8265	$160.83	$160.85	$160.80
Purchase #5	$18.53	4.310%	$19.3286	$19.33	$19.35	$19.30
Purchase #6	$12.59	11.237%	$14.0047	$14.00	$14.00	$14.00
Purchase #7	$23.85	6.583%	$25.42	$25.42	$25.40	$25.40
7 purchase totals =	$688.90		$741.4382	$741.44	$741.50	$741.30