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	$92.61	12.611%	$104.289	$104.29	$104.30	$104.30
Purchase #2	$118.99	11.198%	$132.3145	$132.31	$132.30	$132.30
Purchase #3	$34.91	8.443%	$37.8575	$37.86	$37.85	$37.90
Purchase #4	$112.84	6.357%	$120.0132	$120.01	$120.00	$120.00
Purchase #5	$162.66	9.565%	$178.2184	$178.22	$178.20	$178.20
Purchase #6	$139.79	8.670%	$151.9098	$151.91	$151.90	$151.90
Purchase #7	$53.81	3.151%	$55.5056	$55.51	$55.50	$55.50
7 purchase totals =	$715.61		$780.1080	$780.11	$780.05	$780.10