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	$205.46	12.324%	$230.7809	$230.78	$230.80	$230.80
Purchase #2	$214.76	8.581%	$233.1886	$233.19	$233.20	$233.20
Purchase #3	$166.82	10.623%	$184.5413	$184.54	$184.55	$184.50
Purchase #4	$45.49	11.854%	$50.8824	$50.88	$50.90	$50.90
Purchase #5	$206.58	13.148%	$233.7411	$233.74	$233.75	$233.70
Purchase #6	$113.69	8.474%	$123.3241	$123.32	$123.30	$123.30
Purchase #7	$25.70	6.245%	$27.305	$27.31	$27.30	$27.30
7 purchase totals =	$978.50		$1,083.7634	$1,083.76	$1,083.80	$1,083.70