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	$64.83	6.144%	$68.8132	$68.81	$68.80	$68.80
Purchase #2	$80.97	11.841%	$90.5577	$90.56	$90.55	$90.60
Purchase #3	$157.69	4.582%	$164.9154	$164.92	$164.90	$164.90
Purchase #4	$111.45	9.195%	$121.6978	$121.70	$121.70	$121.70
Purchase #5	$233.30	9.363%	$255.1439	$255.14	$255.15	$255.10
Purchase #6	$240.90	9.218%	$263.1062	$263.11	$263.10	$263.10
Purchase #7	$168.84	10.825%	$187.1169	$187.12	$187.10	$187.10
7 purchase totals =	$1,057.98		$1,151.3511	$1,151.36	$1,151.30	$1,151.30