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	$237.57	12.453%	$267.1546	$267.15	$267.15	$267.20
Purchase #2	$45.32	3.210%	$46.7748	$46.77	$46.75	$46.80
Purchase #3	$100.70	10.521%	$111.2946	$111.29	$111.30	$111.30
Purchase #4	$172.27	5.364%	$181.5106	$181.51	$181.50	$181.50
Purchase #5	$11.78	12.133%	$13.2093	$13.21	$13.20	$13.20
Purchase #6	$98.77	6.601%	$105.2898	$105.29	$105.30	$105.30
Purchase #7	$58.67	12.680%	$66.1094	$66.11	$66.10	$66.10
7 purchase totals =	$725.08		$791.3431	$791.33	$791.30	$791.40