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	$34.64	4.312%	$36.1337	$36.13	$36.15	$36.10
Purchase #2	$88.92	3.298%	$91.8526	$91.85	$91.85	$91.90
Purchase #3	$190.66	8.303%	$206.4905	$206.49	$206.50	$206.50
Purchase #4	$206.81	8.863%	$225.1396	$225.14	$225.15	$225.10
Purchase #5	$180.70	5.696%	$190.9927	$190.99	$191.00	$191.00
Purchase #6	$103.39	8.211%	$111.8794	$111.88	$111.90	$111.90
Purchase #7	$99.71	9.611%	$109.2931	$109.29	$109.30	$109.30
7 purchase totals =	$904.83		$971.7816	$971.77	$971.85	$971.80