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	$107.36	13.388%	$121.7334	$121.73	$121.75	$121.70
Purchase #2	$96.48	3.694%	$100.044	$100.04	$100.05	$100.00
Purchase #3	$127.59	12.761%	$143.8718	$143.87	$143.85	$143.90
Purchase #4	$71.81	9.706%	$78.7799	$78.78	$78.80	$78.80
Purchase #5	$57.51	11.819%	$64.3071	$64.31	$64.30	$64.30
Purchase #6	$86.42	10.684%	$95.6531	$95.65	$95.65	$95.70
Purchase #7	$131.31	5.800%	$138.926	$138.93	$138.95	$138.90
7 purchase totals =	$678.48		$743.3153	$743.31	$743.35	$743.30