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	$69.43	6.182%	$73.7222	$73.72	$73.70	$73.70
Purchase #2	$235.97	10.401%	$260.5132	$260.51	$260.50	$260.50
Purchase #3	$82.70	9.851%	$90.8468	$90.85	$90.85	$90.80
Purchase #4	$137.28	6.332%	$145.9726	$145.97	$145.95	$146.00
Purchase #5	$147.46	9.814%	$161.9317	$161.93	$161.95	$161.90
Purchase #6	$214.33	11.677%	$239.3573	$239.36	$239.35	$239.40
Purchase #7	$43.41	4.196%	$45.2315	$45.23	$45.25	$45.20
7 purchase totals =	$930.58		$1,017.5753	$1,017.57	$1,017.55	$1,017.50