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	$85.87	6.541%	$91.4868	$91.49	$91.50	$91.50
Purchase #2	$162.87	8.604%	$176.8833	$176.88	$176.90	$176.90
Purchase #3	$76.69	5.568%	$80.9601	$80.96	$80.95	$81.00
Purchase #4	$34.74	10.852%	$38.51	$38.51	$38.50	$38.50
Purchase #5	$179.36	9.799%	$196.9355	$196.94	$196.95	$196.90
Purchase #6	$128.34	7.814%	$138.3685	$138.37	$138.35	$138.40
Purchase #7	$45.30	8.676%	$49.2302	$49.23	$49.25	$49.20
7 purchase totals =	$713.17		$772.3744	$772.38	$772.40	$772.40