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	$53.91	4.371%	$56.2664	$56.27	$56.25	$56.30
Purchase #2	$87.98	3.105%	$90.7118	$90.71	$90.70	$90.70
Purchase #3	$56.95	11.394%	$63.4389	$63.44	$63.45	$63.40
Purchase #4	$146.56	4.326%	$152.9002	$152.90	$152.90	$152.90
Purchase #5	$250.33	13.805%	$284.8881	$284.89	$284.90	$284.90
Purchase #6	$48.60	8.768%	$52.8612	$52.86	$52.85	$52.90
Purchase #7	$161.99	4.410%	$169.1338	$169.13	$169.15	$169.10
7 purchase totals =	$806.32		$870.2004	$870.20	$870.20	$870.20