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	$31.77	9.484%	$34.7831	$34.78	$34.80	$34.80
Purchase #2	$243.43	10.594%	$269.219	$269.22	$269.20	$269.20
Purchase #3	$47.30	6.284%	$50.2723	$50.27	$50.25	$50.30
Purchase #4	$208.80	3.281%	$215.6507	$215.65	$215.65	$215.70
Purchase #5	$60.77	11.525%	$67.7737	$67.77	$67.75	$67.80
Purchase #6	$220.30	12.372%	$247.5555	$247.56	$247.55	$247.60
Purchase #7	$43.34	5.141%	$45.5681	$45.57	$45.55	$45.60
7 purchase totals =	$855.71		$930.8224	$930.82	$930.75	$931.00