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	$17.82	3.176%	$18.386	$18.39	$18.40	$18.40
Purchase #2	$62.59	7.334%	$67.1804	$67.18	$67.20	$67.20
Purchase #3	$23.29	9.868%	$25.5883	$25.59	$25.60	$25.60
Purchase #4	$125.49	9.581%	$137.5132	$137.51	$137.50	$137.50
Purchase #5	$130.94	5.495%	$138.1352	$138.14	$138.15	$138.10
Purchase #6	$17.66	4.502%	$18.4551	$18.46	$18.45	$18.50
Purchase #7	$7.72	11.479%	$8.6062	$8.61	$8.60	$8.60
7 purchase totals =	$385.51		$413.8644	$413.88	$413.90	$413.90