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	$105.69	5.506%	$111.5093	$111.51	$111.50	$111.50
Purchase #2	$90.34	3.127%	$93.1649	$93.16	$93.15	$93.20
Purchase #3	$19.91	10.308%	$21.9623	$21.96	$21.95	$22.00
Purchase #4	$63.75	6.270%	$67.7471	$67.75	$67.75	$67.70
Purchase #5	$23.82	7.575%	$25.6244	$25.62	$25.60	$25.60
Purchase #6	$90.59	11.455%	$100.9671	$100.97	$100.95	$101.00
Purchase #7	$170.85	11.676%	$190.7984	$190.80	$190.80	$190.80
7 purchase totals =	$564.95		$611.7735	$611.77	$611.70	$611.80