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	$192.41	5.314%	$202.6347	$202.63	$202.65	$202.60
Purchase #2	$52.83	12.359%	$59.3593	$59.36	$59.35	$59.40
Purchase #3	$148.33	4.247%	$154.6296	$154.63	$154.65	$154.60
Purchase #4	$101.43	7.415%	$108.951	$108.95	$108.95	$109.00
Purchase #5	$40.71	10.772%	$45.0953	$45.10	$45.10	$45.10
Purchase #6	$57.30	4.571%	$59.9192	$59.92	$59.90	$59.90
Purchase #7	$44.57	10.801%	$49.384	$49.38	$49.40	$49.40
7 purchase totals =	$637.58		$679.9731	$679.97	$680.00	$680.00