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	$10.80	3.128%	$11.1378	$11.14	$11.15	$11.10
Purchase #2	$5.89	9.121%	$6.4272	$6.43	$6.45	$6.40
Purchase #3	$104.32	7.426%	$112.0668	$112.07	$112.05	$112.10
Purchase #4	$75.31	6.309%	$80.0613	$80.06	$80.05	$80.10
Purchase #5	$145.92	4.658%	$152.717	$152.72	$152.70	$152.70
Purchase #6	$10.76	6.456%	$11.4547	$11.45	$11.45	$11.50
Purchase #7	$240.51	11.672%	$268.5823	$268.58	$268.60	$268.60
7 purchase totals =	$593.51		$642.4471	$642.45	$642.45	$642.50