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	$52.94	7.467%	$56.893	$56.89	$56.90	$56.90
Purchase #2	$111.96	11.477%	$124.8096	$124.81	$124.80	$124.80
Purchase #3	$89.91	13.531%	$102.0757	$102.08	$102.10	$102.10
Purchase #4	$134.52	12.228%	$150.9691	$150.97	$150.95	$151.00
Purchase #5	$130.81	7.285%	$140.3395	$140.34	$140.35	$140.30
Purchase #6	$156.42	10.532%	$172.8942	$172.89	$172.90	$172.90
Purchase #7	$169.36	13.369%	$192.0017	$192.00	$192.00	$192.00
7 purchase totals =	$845.92		$939.9828	$939.98	$940.00	$940.00