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	$66.80	13.636%	$75.9088	$75.91	$75.90	$75.90
Purchase #2	$186.50	5.588%	$196.9216	$196.92	$196.90	$196.90
Purchase #3	$62.82	6.649%	$66.9969	$67.00	$67.00	$67.00
Purchase #4	$46.45	3.178%	$47.9262	$47.93	$47.95	$47.90
Purchase #5	$188.40	4.405%	$196.699	$196.70	$196.70	$196.70
Purchase #6	$249.53	11.667%	$278.6427	$278.64	$278.65	$278.60
Purchase #7	$105.84	11.777%	$118.3048	$118.30	$118.30	$118.30
7 purchase totals =	$906.34		$981.4000	$981.40	$981.40	$981.30