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	$8.90	4.768%	$9.3244	$9.32	$9.30	$9.30
Purchase #2	$66.28	7.378%	$71.1701	$71.17	$71.15	$71.20
Purchase #3	$53.52	6.254%	$56.8671	$56.87	$56.85	$56.90
Purchase #4	$53.32	4.833%	$55.897	$55.90	$55.90	$55.90
Purchase #5	$232.91	12.808%	$262.7411	$262.74	$262.75	$262.70
Purchase #6	$41.77	6.414%	$44.4491	$44.45	$44.45	$44.40
Purchase #7	$80.77	5.866%	$85.508	$85.51	$85.50	$85.50
7 purchase totals =	$537.47		$585.9568	$585.96	$585.90	$585.90