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	$239.97	13.107%	$271.4229	$271.42	$271.40	$271.40
Purchase #2	$59.96	10.504%	$66.2582	$66.26	$66.25	$66.30
Purchase #3	$195.67	7.504%	$210.3531	$210.35	$210.35	$210.40
Purchase #4	$181.46	13.545%	$206.0388	$206.04	$206.05	$206.00
Purchase #5	$102.95	5.711%	$108.8295	$108.83	$108.85	$108.80
Purchase #6	$51.47	3.182%	$53.1078	$53.11	$53.10	$53.10
Purchase #7	$55.58	7.700%	$59.8597	$59.86	$59.85	$59.90
7 purchase totals =	$887.06		$975.8700	$975.87	$975.85	$975.90