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	$231.67	7.674%	$249.4484	$249.45	$249.45	$249.40
Purchase #2	$34.45	10.475%	$38.0586	$38.06	$38.05	$38.10
Purchase #3	$65.52	8.429%	$71.0427	$71.04	$71.05	$71.00
Purchase #4	$136.91	4.130%	$142.5644	$142.56	$142.55	$142.60
Purchase #5	$147.94	11.615%	$165.1232	$165.12	$165.10	$165.10
Purchase #6	$130.86	11.535%	$145.9547	$145.95	$145.95	$146.00
Purchase #7	$24.62	13.266%	$27.8861	$27.89	$27.90	$27.90
7 purchase totals =	$771.97		$840.0781	$840.07	$840.05	$840.10