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	$17.81	13.644%	$20.24	$20.24	$20.25	$20.20
Purchase #2	$88.77	7.870%	$95.7562	$95.76	$95.75	$95.80
Purchase #3	$63.56	13.816%	$72.3414	$72.34	$72.35	$72.30
Purchase #4	$17.48	9.432%	$19.1287	$19.13	$19.15	$19.10
Purchase #5	$63.96	13.311%	$72.4737	$72.47	$72.45	$72.50
Purchase #6	$228.33	10.614%	$252.5649	$252.56	$252.55	$252.60
Purchase #7	$231.65	7.493%	$249.0075	$249.01	$249.00	$249.00
7 purchase totals =	$711.56		$781.5124	$781.51	$781.50	$781.50