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	$50.56	12.363%	$56.8107	$56.81	$56.80	$56.80
Purchase #2	$152.78	8.396%	$165.6074	$165.61	$165.60	$165.60
Purchase #3	$240.38	12.651%	$270.7905	$270.79	$270.80	$270.80
Purchase #4	$158.81	7.549%	$170.7986	$170.80	$170.80	$170.80
Purchase #5	$115.45	10.604%	$127.6923	$127.69	$127.70	$127.70
Purchase #6	$88.86	13.737%	$101.0667	$101.07	$101.05	$101.10
Purchase #7	$108.89	6.752%	$116.2423	$116.24	$116.25	$116.20
7 purchase totals =	$915.73		$1,009.0085	$1,009.01	$1,009.00	$1,009.00