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	$29.47	3.836%	$30.6005	$30.60	$30.60	$30.60
Purchase #2	$162.79	10.484%	$179.8569	$179.86	$179.85	$179.90
Purchase #3	$103.82	7.325%	$111.4248	$111.42	$111.40	$111.40
Purchase #4	$221.73	3.623%	$229.7633	$229.76	$229.75	$229.80
Purchase #5	$249.76	12.143%	$280.0884	$280.09	$280.10	$280.10
Purchase #6	$5.78	5.590%	$6.1031	$6.10	$6.10	$6.10
Purchase #7	$84.41	11.855%	$94.4168	$94.42	$94.40	$94.40
7 purchase totals =	$857.76		$932.2538	$932.25	$932.20	$932.30