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	$107.66	11.421%	$119.9558	$119.96	$119.95	$120.00
Purchase #2	$147.52	5.368%	$155.4389	$155.44	$155.45	$155.40
Purchase #3	$250.32	10.217%	$275.8952	$275.90	$275.90	$275.90
Purchase #4	$242.32	12.176%	$271.8249	$271.82	$271.80	$271.80
Purchase #5	$106.41	9.533%	$116.5541	$116.55	$116.55	$116.60
Purchase #6	$27.65	5.256%	$29.1033	$29.10	$29.10	$29.10
Purchase #7	$40.83	6.450%	$43.4635	$43.46	$43.45	$43.50
7 purchase totals =	$922.71		$1,012.2357	$1,012.23	$1,012.20	$1,012.30