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	$104.41	12.840%	$117.8162	$117.82	$117.80	$117.80
Purchase #2	$123.98	12.188%	$139.0907	$139.09	$139.10	$139.10
Purchase #3	$130.33	13.157%	$147.4775	$147.48	$147.50	$147.50
Purchase #4	$5.45	8.226%	$5.8983	$5.90	$5.90	$5.90
Purchase #5	$72.56	11.180%	$80.6722	$80.67	$80.65	$80.70
Purchase #6	$18.85	8.318%	$20.4179	$20.42	$20.40	$20.40
Purchase #7	$187.93	10.751%	$208.1344	$208.13	$208.15	$208.10
7 purchase totals =	$643.51		$719.5072	$719.51	$719.50	$719.50