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	$130.52	8.160%	$141.1704	$141.17	$141.15	$141.20
Purchase #2	$149.43	10.214%	$164.6928	$164.69	$164.70	$164.70
Purchase #3	$37.63	13.191%	$42.5938	$42.59	$42.60	$42.60
Purchase #4	$15.44	10.106%	$17.0004	$17.00	$17.00	$17.00
Purchase #5	$39.85	9.297%	$43.5549	$43.55	$43.55	$43.60
Purchase #6	$178.37	11.503%	$198.8879	$198.89	$198.90	$198.90
Purchase #7	$78.79	5.553%	$83.1652	$83.17	$83.15	$83.20
7 purchase totals =	$630.03		$691.0654	$691.06	$691.05	$691.20