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	$103.49	8.544%	$112.3322	$112.33	$112.35	$112.30
Purchase #2	$250.26	13.694%	$284.5306	$284.53	$284.55	$284.50
Purchase #3	$139.92	12.105%	$156.8573	$156.86	$156.85	$156.90
Purchase #4	$139.85	8.794%	$152.1484	$152.15	$152.15	$152.10
Purchase #5	$183.56	5.256%	$193.2079	$193.21	$193.20	$193.20
Purchase #6	$7.41	6.596%	$7.8988	$7.90	$7.90	$7.90
Purchase #7	$64.83	10.181%	$71.4303	$71.43	$71.45	$71.40
7 purchase totals =	$889.32		$978.4055	$978.41	$978.45	$978.30