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	$75.54	3.860%	$78.4558	$78.46	$78.45	$78.50
Purchase #2	$24.74	9.858%	$27.1789	$27.18	$27.20	$27.20
Purchase #3	$24.33	9.246%	$26.5796	$26.58	$26.60	$26.60
Purchase #4	$52.47	9.663%	$57.5402	$57.54	$57.55	$57.50
Purchase #5	$78.90	11.544%	$88.0082	$88.01	$88.00	$88.00
Purchase #6	$83.92	8.841%	$91.3394	$91.34	$91.35	$91.30
Purchase #7	$100.71	13.255%	$114.0591	$114.06	$114.05	$114.10
7 purchase totals =	$440.61		$483.1612	$483.17	$483.20	$483.20