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	$95.27	5.618%	$100.6223	$100.62	$100.60	$100.60
Purchase #2	$85.81	5.500%	$90.5296	$90.53	$90.55	$90.50
Purchase #3	$40.86	12.482%	$45.9601	$45.96	$45.95	$46.00
Purchase #4	$250.99	10.818%	$278.1421	$278.14	$278.15	$278.10
Purchase #5	$95.63	5.397%	$100.7912	$100.79	$100.80	$100.80
Purchase #6	$213.45	8.754%	$232.1354	$232.14	$232.15	$232.10
Purchase #7	$87.53	4.393%	$91.3752	$91.38	$91.40	$91.40
7 purchase totals =	$869.54		$939.5559	$939.56	$939.60	$939.50