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	$142.56	13.365%	$161.6131	$161.61	$161.60	$161.60
Purchase #2	$248.77	12.544%	$279.9757	$279.98	$280.00	$280.00
Purchase #3	$57.64	8.569%	$62.5792	$62.58	$62.60	$62.60
Purchase #4	$57.93	3.218%	$59.7942	$59.79	$59.80	$59.80
Purchase #5	$228.76	5.816%	$242.0647	$242.06	$242.05	$242.10
Purchase #6	$85.76	4.342%	$89.4837	$89.48	$89.50	$89.50
Purchase #7	$156.89	13.484%	$178.045	$178.05	$178.05	$178.00
7 purchase totals =	$978.31		$1,073.5556	$1,073.55	$1,073.60	$1,073.60