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	$202.72	13.299%	$229.6797	$229.68	$229.70	$229.70
Purchase #2	$96.26	13.113%	$108.8826	$108.88	$108.90	$108.90
Purchase #3	$100.37	10.872%	$111.2822	$111.28	$111.30	$111.30
Purchase #4	$59.69	13.808%	$67.932	$67.93	$67.95	$67.90
Purchase #5	$126.30	13.176%	$142.9413	$142.94	$142.95	$142.90
Purchase #6	$209.30	12.612%	$235.6969	$235.70	$235.70	$235.70
Purchase #7	$58.27	9.104%	$63.5749	$63.57	$63.55	$63.60
7 purchase totals =	$852.91		$959.9896	$959.98	$960.05	$960.00