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	$128.28	7.371%	$137.7355	$137.74	$137.75	$137.70
Purchase #2	$171.42	6.458%	$182.4903	$182.49	$182.50	$182.50
Purchase #3	$229.47	7.146%	$245.8679	$245.87	$245.85	$245.90
Purchase #4	$109.67	3.598%	$113.6159	$113.62	$113.60	$113.60
Purchase #5	$195.78	13.575%	$222.3571	$222.36	$222.35	$222.40
Purchase #6	$22.70	10.607%	$25.1078	$25.11	$25.10	$25.10
Purchase #7	$123.67	8.634%	$134.3477	$134.35	$134.35	$134.30
7 purchase totals =	$980.99		$1,061.5222	$1,061.54	$1,061.50	$1,061.50