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	$98.55	6.845%	$105.2957	$105.30	$105.30	$105.30
Purchase #2	$36.54	10.633%	$40.4253	$40.43	$40.45	$40.40
Purchase #3	$243.35	9.144%	$265.6019	$265.60	$265.60	$265.60
Purchase #4	$63.79	12.564%	$71.8046	$71.80	$71.80	$71.80
Purchase #5	$101.78	9.654%	$111.6058	$111.61	$111.60	$111.60
Purchase #6	$11.69	11.849%	$13.0751	$13.08	$13.10	$13.10
Purchase #7	$143.93	5.822%	$152.3096	$152.31	$152.30	$152.30
7 purchase totals =	$699.63		$760.1180	$760.13	$760.15	$760.10