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	$178.38	12.156%	$200.0639	$200.06	$200.05	$200.10
Purchase #2	$169.58	12.504%	$190.7843	$190.78	$190.80	$190.80
Purchase #3	$49.57	5.181%	$52.1382	$52.14	$52.15	$52.10
Purchase #4	$220.98	8.108%	$238.8971	$238.90	$238.90	$238.90
Purchase #5	$248.55	12.687%	$280.0835	$280.08	$280.10	$280.10
Purchase #6	$50.42	10.531%	$55.7297	$55.73	$55.75	$55.70
Purchase #7	$248.37	6.344%	$264.1266	$264.13	$264.15	$264.10
7 purchase totals =	$1,165.85		$1,281.8233	$1,281.82	$1,281.90	$1,281.80