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	$248.34	6.236%	$263.8265	$263.83	$263.85	$263.80
Purchase #2	$209.56	4.396%	$218.7723	$218.77	$218.75	$218.80
Purchase #3	$103.65	7.148%	$111.0589	$111.06	$111.05	$111.10
Purchase #4	$67.81	9.755%	$74.4249	$74.42	$74.40	$74.40
Purchase #5	$26.76	3.138%	$27.5997	$27.60	$27.60	$27.60
Purchase #6	$136.70	10.316%	$150.802	$150.80	$150.80	$150.80
Purchase #7	$210.87	10.620%	$233.2644	$233.26	$233.25	$233.30
7 purchase totals =	$1,003.69		$1,079.7487	$1,079.74	$1,079.70	$1,079.80