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	$113.43	3.250%	$117.1165	$117.12	$117.10	$117.10
Purchase #2	$141.70	10.738%	$156.9157	$156.92	$156.90	$156.90
Purchase #3	$173.54	6.370%	$184.5945	$184.59	$184.60	$184.60
Purchase #4	$88.36	13.691%	$100.4574	$100.46	$100.45	$100.50
Purchase #5	$151.85	4.295%	$158.372	$158.37	$158.35	$158.40
Purchase #6	$74.93	10.232%	$82.5968	$82.60	$82.60	$82.60
Purchase #7	$206.67	10.164%	$227.6759	$227.68	$227.70	$227.70
7 purchase totals =	$950.48		$1,027.7288	$1,027.74	$1,027.70	$1,027.80