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	$41.35	10.802%	$45.8166	$45.82	$45.80	$45.80
Purchase #2	$35.98	5.545%	$37.9751	$37.98	$38.00	$38.00
Purchase #3	$44.25	9.271%	$48.3524	$48.35	$48.35	$48.40
Purchase #4	$190.82	11.154%	$212.1041	$212.10	$212.10	$212.10
Purchase #5	$6.70	10.370%	$7.3948	$7.39	$7.40	$7.40
Purchase #6	$59.48	6.769%	$63.5062	$63.51	$63.50	$63.50
Purchase #7	$160.67	11.628%	$179.3527	$179.35	$179.35	$179.40
7 purchase totals =	$539.25		$594.5019	$594.50	$594.50	$594.60