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	$127.41	10.358%	$140.6071	$140.61	$140.60	$140.60
Purchase #2	$148.86	9.246%	$162.6236	$162.62	$162.60	$162.60
Purchase #3	$94.31	12.160%	$105.7781	$105.78	$105.80	$105.80
Purchase #4	$76.33	10.375%	$84.2492	$84.25	$84.25	$84.20
Purchase #5	$28.96	9.845%	$31.8111	$31.81	$31.80	$31.80
Purchase #6	$188.99	12.208%	$212.0619	$212.06	$212.05	$212.10
Purchase #7	$131.69	10.801%	$145.9138	$145.91	$145.90	$145.90
7 purchase totals =	$796.55		$883.0448	$883.04	$883.00	$883.00