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	$144.44	4.661%	$151.1723	$151.17	$151.15	$151.20
Purchase #2	$33.35	13.168%	$37.7415	$37.74	$37.75	$37.70
Purchase #3	$203.28	6.281%	$216.048	$216.05	$216.05	$216.00
Purchase #4	$76.31	9.546%	$83.5946	$83.59	$83.60	$83.60
Purchase #5	$50.89	10.361%	$56.1627	$56.16	$56.15	$56.20
Purchase #6	$188.47	9.852%	$207.0381	$207.04	$207.05	$207.00
Purchase #7	$78.67	13.408%	$89.2181	$89.22	$89.20	$89.20
7 purchase totals =	$775.41		$840.9753	$840.97	$840.95	$840.90