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	$27.28	3.346%	$28.1928	$28.19	$28.20	$28.20
Purchase #2	$247.39	9.380%	$270.5952	$270.60	$270.60	$270.60
Purchase #3	$18.58	10.265%	$20.4872	$20.49	$20.50	$20.50
Purchase #4	$96.82	3.196%	$99.9144	$99.91	$99.90	$99.90
Purchase #5	$162.51	4.535%	$169.8798	$169.88	$169.90	$169.90
Purchase #6	$235.82	12.816%	$266.0427	$266.04	$266.05	$266.00
Purchase #7	$157.63	10.249%	$173.7855	$173.79	$173.80	$173.80
7 purchase totals =	$946.03		$1,028.8976	$1,028.90	$1,028.95	$1,028.90