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	$35.47	13.351%	$40.2056	$40.21	$40.20	$40.20
Purchase #2	$81.96	6.561%	$87.3374	$87.34	$87.35	$87.30
Purchase #3	$101.78	13.306%	$115.3228	$115.32	$115.30	$115.30
Purchase #4	$56.43	5.470%	$59.5167	$59.52	$59.50	$59.50
Purchase #5	$90.98	10.837%	$100.8395	$100.84	$100.85	$100.80
Purchase #6	$64.47	4.783%	$67.5536	$67.55	$67.55	$67.60
Purchase #7	$249.57	10.286%	$275.2408	$275.24	$275.25	$275.20
7 purchase totals =	$680.66		$746.0164	$746.02	$746.00	$745.90