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	$150.61	12.158%	$168.9212	$168.92	$168.90	$168.90
Purchase #2	$140.95	3.551%	$145.9551	$145.96	$145.95	$146.00
Purchase #3	$32.82	4.373%	$34.2552	$34.26	$34.25	$34.30
Purchase #4	$184.48	12.435%	$207.4201	$207.42	$207.40	$207.40
Purchase #5	$170.52	3.138%	$175.8709	$175.87	$175.85	$175.90
Purchase #6	$187.51	3.201%	$193.5122	$193.51	$193.50	$193.50
Purchase #7	$163.65	13.484%	$185.7166	$185.72	$185.70	$185.70
7 purchase totals =	$1,030.54		$1,111.6513	$1,111.66	$1,111.55	$1,111.70