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	$178.78	6.211%	$189.884	$189.88	$189.90	$189.90
Purchase #2	$218.28	7.264%	$234.1359	$234.14	$234.15	$234.10
Purchase #3	$140.63	7.328%	$150.9354	$150.94	$150.95	$150.90
Purchase #4	$54.45	12.182%	$61.0831	$61.08	$61.10	$61.10
Purchase #5	$37.75	12.792%	$42.579	$42.58	$42.60	$42.60
Purchase #6	$188.28	12.332%	$211.4987	$211.50	$211.50	$211.50
Purchase #7	$137.49	10.496%	$151.921	$151.92	$151.90	$151.90
7 purchase totals =	$955.66		$1,042.0371	$1,042.04	$1,042.10	$1,042.00