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	$80.46	10.679%	$89.0523	$89.05	$89.05	$89.10
Purchase #2	$27.34	4.385%	$28.5389	$28.54	$28.55	$28.50
Purchase #3	$215.37	13.678%	$244.8283	$244.83	$244.85	$244.80
Purchase #4	$196.88	7.627%	$211.896	$211.90	$211.90	$211.90
Purchase #5	$210.91	10.698%	$233.4732	$233.47	$233.45	$233.50
Purchase #6	$230.53	3.660%	$238.9674	$238.97	$238.95	$239.00
Purchase #7	$199.45	6.412%	$212.2387	$212.24	$212.25	$212.20
7 purchase totals =	$1,160.94		$1,258.9948	$1,259.00	$1,259.00	$1,259.00