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	$85.34	10.270%	$94.1044	$94.10	$94.10	$94.10
Purchase #2	$35.91	10.281%	$39.6019	$39.60	$39.60	$39.60
Purchase #3	$218.64	5.770%	$231.2555	$231.26	$231.25	$231.30
Purchase #4	$188.75	8.203%	$204.2332	$204.23	$204.25	$204.20
Purchase #5	$138.39	11.566%	$154.3962	$154.40	$154.40	$154.40
Purchase #6	$54.40	8.686%	$59.1252	$59.13	$59.15	$59.10
Purchase #7	$67.80	6.831%	$72.4314	$72.43	$72.45	$72.40
7 purchase totals =	$789.23		$855.1478	$855.15	$855.20	$855.10