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	$159.94	12.139%	$179.3551	$179.36	$179.35	$179.40
Purchase #2	$93.29	6.531%	$99.3828	$99.38	$99.40	$99.40
Purchase #3	$247.38	9.324%	$270.4457	$270.45	$270.45	$270.40
Purchase #4	$41.80	3.113%	$43.1012	$43.10	$43.10	$43.10
Purchase #5	$58.36	5.285%	$61.4443	$61.44	$61.45	$61.40
Purchase #6	$85.82	11.624%	$95.7957	$95.80	$95.80	$95.80
Purchase #7	$43.45	6.750%	$46.3829	$46.38	$46.40	$46.40
7 purchase totals =	$730.04		$795.9077	$795.91	$795.95	$795.90