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	$246.58	12.873%	$278.3222	$278.32	$278.30	$278.30
Purchase #2	$42.88	4.853%	$44.961	$44.96	$44.95	$45.00
Purchase #3	$11.41	4.856%	$11.9641	$11.96	$11.95	$12.00
Purchase #4	$140.41	8.625%	$152.5204	$152.52	$152.50	$152.50
Purchase #5	$83.39	3.199%	$86.0576	$86.06	$86.05	$86.10
Purchase #6	$150.65	5.425%	$158.8228	$158.82	$158.80	$158.80
Purchase #7	$238.37	9.547%	$261.1272	$261.13	$261.15	$261.10
7 purchase totals =	$913.69		$993.7753	$993.77	$993.70	$993.80