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	$71.48	10.491%	$78.979	$78.98	$79.00	$79.00
Purchase #2	$65.37	11.438%	$72.847	$72.85	$72.85	$72.80
Purchase #3	$72.72	11.138%	$80.8196	$80.82	$80.80	$80.80
Purchase #4	$223.79	5.745%	$236.6467	$236.65	$236.65	$236.60
Purchase #5	$69.77	8.343%	$75.5909	$75.59	$75.60	$75.60
Purchase #6	$26.85	12.308%	$30.1547	$30.15	$30.15	$30.20
Purchase #7	$99.75	11.367%	$111.0886	$111.09	$111.10	$111.10
7 purchase totals =	$629.73		$686.1265	$686.13	$686.15	$686.10