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	$11.79	3.394%	$12.1902	$12.19	$12.20	$12.20
Purchase #2	$62.80	7.630%	$67.5916	$67.59	$67.60	$67.60
Purchase #3	$67.44	7.472%	$72.4791	$72.48	$72.50	$72.50
Purchase #4	$99.72	10.338%	$110.0291	$110.03	$110.05	$110.00
Purchase #5	$107.71	3.154%	$111.1072	$111.11	$111.10	$111.10
Purchase #6	$136.69	11.451%	$152.3424	$152.34	$152.35	$152.30
Purchase #7	$105.60	10.232%	$116.405	$116.41	$116.40	$116.40
7 purchase totals =	$591.75		$642.1446	$642.15	$642.20	$642.10