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	$85.45	6.170%	$90.7223	$90.72	$90.70	$90.70
Purchase #2	$211.98	10.307%	$233.8288	$233.83	$233.85	$233.80
Purchase #3	$179.55	7.654%	$193.2928	$193.29	$193.30	$193.30
Purchase #4	$220.88	6.825%	$235.9551	$235.96	$235.95	$236.00
Purchase #5	$43.30	5.245%	$45.5711	$45.57	$45.55	$45.60
Purchase #6	$199.34	9.681%	$218.6381	$218.64	$218.65	$218.60
Purchase #7	$204.54	8.683%	$222.3002	$222.30	$222.30	$222.30
7 purchase totals =	$1,145.04		$1,240.3084	$1,240.31	$1,240.30	$1,240.30