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	$85.41	7.114%	$91.4861	$91.49	$91.50	$91.50
Purchase #2	$28.85	11.545%	$32.1807	$32.18	$32.20	$32.20
Purchase #3	$178.31	11.469%	$198.7604	$198.76	$198.75	$198.80
Purchase #4	$110.82	11.776%	$123.8702	$123.87	$123.85	$123.90
Purchase #5	$5.84	10.482%	$6.4521	$6.45	$6.45	$6.50
Purchase #6	$24.52	5.704%	$25.9186	$25.92	$25.90	$25.90
Purchase #7	$43.68	5.122%	$45.9173	$45.92	$45.90	$45.90
7 purchase totals =	$477.43		$524.5854	$524.59	$524.55	$524.70