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	$238.77	11.497%	$266.2214	$266.22	$266.20	$266.20
Purchase #2	$117.48	4.576%	$122.8559	$122.86	$122.85	$122.90
Purchase #3	$236.64	7.448%	$254.2649	$254.26	$254.25	$254.30
Purchase #4	$57.56	4.834%	$60.3425	$60.34	$60.35	$60.30
Purchase #5	$110.82	5.480%	$116.8929	$116.89	$116.90	$116.90
Purchase #6	$134.80	8.407%	$146.1326	$146.13	$146.15	$146.10
Purchase #7	$86.59	3.873%	$89.9436	$89.94	$89.95	$89.90
7 purchase totals =	$982.66		$1,056.6538	$1,056.64	$1,056.65	$1,056.60