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	$16.97	5.251%	$17.8611	$17.86	$17.85	$17.90
Purchase #2	$61.79	9.873%	$67.8905	$67.89	$67.90	$67.90
Purchase #3	$143.90	5.537%	$151.8677	$151.87	$151.85	$151.90
Purchase #4	$239.53	13.752%	$272.4702	$272.47	$272.45	$272.50
Purchase #5	$69.62	10.616%	$77.0109	$77.01	$77.00	$77.00
Purchase #6	$93.71	7.738%	$100.9613	$100.96	$100.95	$101.00
Purchase #7	$62.42	7.777%	$67.2744	$67.27	$67.25	$67.30
7 purchase totals =	$687.94		$755.3361	$755.33	$755.25	$755.50