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	$13.96	11.845%	$15.6136	$15.61	$15.60	$15.60
Purchase #2	$59.98	10.132%	$66.0572	$66.06	$66.05	$66.10
Purchase #3	$113.33	9.402%	$123.9853	$123.99	$124.00	$124.00
Purchase #4	$106.25	3.199%	$109.6489	$109.65	$109.65	$109.60
Purchase #5	$85.49	4.707%	$89.514	$89.51	$89.50	$89.50
Purchase #6	$88.75	6.729%	$94.722	$94.72	$94.70	$94.70
Purchase #7	$199.76	12.358%	$224.4463	$224.45	$224.45	$224.40
7 purchase totals =	$667.52		$723.9873	$723.99	$723.95	$723.90