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	$81.28	12.546%	$91.4774	$91.48	$91.50	$91.50
Purchase #2	$45.48	5.273%	$47.8782	$47.88	$47.90	$47.90
Purchase #3	$157.34	10.253%	$173.4721	$173.47	$173.45	$173.50
Purchase #4	$36.98	11.114%	$41.09	$41.09	$41.10	$41.10
Purchase #5	$59.78	5.294%	$62.9448	$62.94	$62.95	$62.90
Purchase #6	$178.66	7.120%	$191.3806	$191.38	$191.40	$191.40
Purchase #7	$45.27	5.192%	$47.6204	$47.62	$47.60	$47.60
7 purchase totals =	$604.79		$655.8635	$655.86	$655.90	$655.90