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	$136.84	8.538%	$148.5234	$148.52	$148.50	$148.50
Purchase #2	$63.29	3.219%	$65.3273	$65.33	$65.35	$65.30
Purchase #3	$95.98	13.157%	$108.6081	$108.61	$108.60	$108.60
Purchase #4	$188.37	5.700%	$199.1071	$199.11	$199.10	$199.10
Purchase #5	$215.43	5.817%	$227.9616	$227.96	$227.95	$228.00
Purchase #6	$153.34	12.452%	$172.4339	$172.43	$172.45	$172.40
Purchase #7	$128.78	4.753%	$134.9009	$134.90	$134.90	$134.90
7 purchase totals =	$982.03		$1,056.8623	$1,056.86	$1,056.85	$1,056.80