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	$27.60	3.450%	$28.5522	$28.55	$28.55	$28.60
Purchase #2	$57.96	13.524%	$65.7985	$65.80	$65.80	$65.80
Purchase #3	$127.98	4.154%	$133.2963	$133.30	$133.30	$133.30
Purchase #4	$35.32	11.432%	$39.3578	$39.36	$39.35	$39.40
Purchase #5	$147.98	9.357%	$161.8265	$161.83	$161.85	$161.80
Purchase #6	$148.69	6.737%	$158.7072	$158.71	$158.70	$158.70
Purchase #7	$73.36	6.341%	$78.0118	$78.01	$78.00	$78.00
7 purchase totals =	$618.89		$665.5503	$665.56	$665.55	$665.60