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	$18.79	11.469%	$20.945	$20.95	$20.95	$20.90
Purchase #2	$95.41	6.108%	$101.2376	$101.24	$101.25	$101.20
Purchase #3	$29.61	6.454%	$31.521	$31.52	$31.50	$31.50
Purchase #4	$151.72	13.254%	$171.829	$171.83	$171.85	$171.80
Purchase #5	$210.61	9.479%	$230.5737	$230.57	$230.55	$230.60
Purchase #6	$7.99	11.257%	$8.8894	$8.89	$8.90	$8.90
Purchase #7	$241.59	5.837%	$255.6916	$255.69	$255.70	$255.70
7 purchase totals =	$755.72		$820.6873	$820.69	$820.70	$820.60