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	$132.40	3.391%	$136.8897	$136.89	$136.90	$136.90
Purchase #2	$62.40	7.518%	$67.0912	$67.09	$67.10	$67.10
Purchase #3	$27.49	8.537%	$29.8368	$29.84	$29.85	$29.80
Purchase #4	$26.76	13.627%	$30.4066	$30.41	$30.40	$30.40
Purchase #5	$71.89	8.493%	$77.9956	$78.00	$78.00	$78.00
Purchase #6	$104.59	11.298%	$116.4066	$116.41	$116.40	$116.40
Purchase #7	$6.98	12.393%	$7.845	$7.85	$7.85	$7.80
7 purchase totals =	$432.51		$466.4715	$466.49	$466.50	$466.40