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	$10.52	3.163%	$10.8527	$10.85	$10.85	$10.90
Purchase #2	$23.35	5.868%	$24.7202	$24.72	$24.70	$24.70
Purchase #3	$233.33	10.264%	$257.279	$257.28	$257.30	$257.30
Purchase #4	$50.86	7.372%	$54.6094	$54.61	$54.60	$54.60
Purchase #5	$28.67	8.449%	$31.0923	$31.09	$31.10	$31.10
Purchase #6	$63.80	12.484%	$71.7648	$71.76	$71.75	$71.80
Purchase #7	$83.87	9.107%	$91.508	$91.51	$91.50	$91.50
7 purchase totals =	$494.40		$541.8264	$541.82	$541.80	$541.90