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	$49.84	6.481%	$53.0701	$53.07	$53.05	$53.10
Purchase #2	$37.59	3.160%	$38.7778	$38.78	$38.80	$38.80
Purchase #3	$90.97	11.165%	$101.1268	$101.13	$101.15	$101.10
Purchase #4	$41.35	10.344%	$45.6272	$45.63	$45.65	$45.60
Purchase #5	$89.64	10.351%	$98.9186	$98.92	$98.90	$98.90
Purchase #6	$214.52	3.190%	$221.3632	$221.36	$221.35	$221.40
Purchase #7	$10.40	11.687%	$11.6154	$11.62	$11.60	$11.60
7 purchase totals =	$534.31		$570.4991	$570.51	$570.50	$570.50