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	$17.88	5.211%	$18.8117	$18.81	$18.80	$18.80
Purchase #2	$243.79	9.134%	$266.0578	$266.06	$266.05	$266.10
Purchase #3	$235.80	4.280%	$245.8922	$245.89	$245.90	$245.90
Purchase #4	$58.77	11.675%	$65.6314	$65.63	$65.65	$65.60
Purchase #5	$84.64	5.333%	$89.1539	$89.15	$89.15	$89.20
Purchase #6	$156.78	8.151%	$169.5591	$169.56	$169.55	$169.60
Purchase #7	$114.59	11.540%	$127.8137	$127.81	$127.80	$127.80
7 purchase totals =	$912.25		$982.9198	$982.91	$982.90	$983.00