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	$26.34	4.721%	$27.5835	$27.58	$27.60	$27.60
Purchase #2	$132.43	10.607%	$146.4769	$146.48	$146.50	$146.50
Purchase #3	$179.71	5.535%	$189.6569	$189.66	$189.65	$189.70
Purchase #4	$70.88	7.564%	$76.2414	$76.24	$76.25	$76.20
Purchase #5	$15.89	6.428%	$16.9114	$16.91	$16.90	$16.90
Purchase #6	$64.71	10.661%	$71.6087	$71.61	$71.60	$71.60
Purchase #7	$131.85	5.382%	$138.9462	$138.95	$138.95	$138.90
7 purchase totals =	$621.81		$667.4250	$667.43	$667.45	$667.40