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	$246.45	13.672%	$280.1446	$280.14	$280.15	$280.10
Purchase #2	$143.98	3.523%	$149.0524	$149.05	$149.05	$149.10
Purchase #3	$67.47	13.405%	$76.5144	$76.51	$76.50	$76.50
Purchase #4	$91.73	8.127%	$99.1849	$99.18	$99.20	$99.20
Purchase #5	$25.67	12.103%	$28.7768	$28.78	$28.80	$28.80
Purchase #6	$174.48	5.592%	$184.2369	$184.24	$184.25	$184.20
Purchase #7	$79.64	3.400%	$82.3478	$82.35	$82.35	$82.30
7 purchase totals =	$829.42		$900.2578	$900.25	$900.30	$900.20