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	$90.25	7.624%	$97.1307	$97.13	$97.15	$97.10
Purchase #2	$42.51	3.760%	$44.1084	$44.11	$44.10	$44.10
Purchase #3	$72.66	8.400%	$78.7634	$78.76	$78.75	$78.80
Purchase #4	$43.31	9.193%	$47.2915	$47.29	$47.30	$47.30
Purchase #5	$21.31	13.761%	$24.2425	$24.24	$24.25	$24.20
Purchase #6	$191.94	6.553%	$204.5178	$204.52	$204.50	$204.50
Purchase #7	$78.50	9.567%	$86.0101	$86.01	$86.00	$86.00
7 purchase totals =	$540.48		$582.0644	$582.06	$582.05	$582.00