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	$125.47	11.384%	$139.7535	$139.75	$139.75	$139.80
Purchase #2	$34.58	13.602%	$39.2836	$39.28	$39.30	$39.30
Purchase #3	$139.66	12.337%	$156.8899	$156.89	$156.90	$156.90
Purchase #4	$40.76	13.872%	$46.4142	$46.41	$46.40	$46.40
Purchase #5	$107.54	12.439%	$120.9169	$120.92	$120.90	$120.90
Purchase #6	$71.35	9.465%	$78.1033	$78.10	$78.10	$78.10
Purchase #7	$219.59	13.497%	$249.2281	$249.23	$249.25	$249.20
7 purchase totals =	$738.95		$830.5895	$830.58	$830.60	$830.60