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	$41.27	3.182%	$42.5832	$42.58	$42.60	$42.60
Purchase #2	$182.34	5.361%	$192.1152	$192.12	$192.10	$192.10
Purchase #3	$33.33	3.273%	$34.4209	$34.42	$34.40	$34.40
Purchase #4	$156.96	5.256%	$165.2098	$165.21	$165.20	$165.20
Purchase #5	$100.31	3.726%	$104.0476	$104.05	$104.05	$104.00
Purchase #6	$98.70	10.673%	$109.2343	$109.23	$109.25	$109.20
Purchase #7	$108.67	8.684%	$118.1069	$118.11	$118.10	$118.10
7 purchase totals =	$721.58		$765.7179	$765.72	$765.70	$765.60