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	$17.88	6.472%	$19.0372	$19.04	$19.05	$19.00
Purchase #2	$169.38	12.710%	$190.9082	$190.91	$190.90	$190.90
Purchase #3	$63.80	13.184%	$72.2114	$72.21	$72.20	$72.20
Purchase #4	$18.52	3.231%	$19.1184	$19.12	$19.10	$19.10
Purchase #5	$91.75	13.630%	$104.2555	$104.26	$104.25	$104.30
Purchase #6	$143.36	5.411%	$151.1172	$151.12	$151.10	$151.10
Purchase #7	$248.77	9.732%	$272.9803	$272.98	$273.00	$273.00
7 purchase totals =	$753.46		$829.6282	$829.64	$829.60	$829.60