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	$248.39	10.254%	$273.8599	$273.86	$273.85	$273.90
Purchase #2	$146.71	4.347%	$153.0875	$153.09	$153.10	$153.10
Purchase #3	$161.35	12.469%	$181.4687	$181.47	$181.45	$181.50
Purchase #4	$37.81	12.462%	$42.5219	$42.52	$42.50	$42.50
Purchase #5	$77.28	4.184%	$80.5134	$80.51	$80.50	$80.50
Purchase #6	$127.68	10.362%	$140.9102	$140.91	$140.90	$140.90
Purchase #7	$48.32	5.314%	$50.8877	$50.89	$50.90	$50.90
7 purchase totals =	$847.54		$923.2493	$923.25	$923.20	$923.30