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	$141.27	6.505%	$150.4596	$150.46	$150.45	$150.50
Purchase #2	$79.40	4.781%	$83.1961	$83.20	$83.20	$83.20
Purchase #3	$43.80	9.127%	$47.7976	$47.80	$47.80	$47.80
Purchase #4	$78.37	8.455%	$84.9962	$85.00	$85.00	$85.00
Purchase #5	$17.88	5.312%	$18.8298	$18.83	$18.85	$18.80
Purchase #6	$106.66	4.717%	$111.6912	$111.69	$111.70	$111.70
Purchase #7	$40.74	12.466%	$45.8186	$45.82	$45.80	$45.80
7 purchase totals =	$508.12		$542.7891	$542.80	$542.80	$542.80