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	$46.89	12.199%	$52.6101	$52.61	$52.60	$52.60
Purchase #2	$122.86	4.307%	$128.1516	$128.15	$128.15	$128.20
Purchase #3	$237.74	11.290%	$264.5808	$264.58	$264.60	$264.60
Purchase #4	$63.65	13.126%	$72.0047	$72.00	$72.00	$72.00
Purchase #5	$207.96	7.223%	$222.981	$222.98	$223.00	$223.00
Purchase #6	$38.41	8.308%	$41.6011	$41.60	$41.60	$41.60
Purchase #7	$205.46	5.805%	$217.387	$217.39	$217.40	$217.40
7 purchase totals =	$922.97		$999.3163	$999.31	$999.35	$999.40