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	$107.93	9.579%	$118.2686	$118.27	$118.25	$118.30
Purchase #2	$104.60	9.780%	$114.8299	$114.83	$114.85	$114.80
Purchase #3	$183.61	6.411%	$195.3812	$195.38	$195.40	$195.40
Purchase #4	$71.78	4.180%	$74.7804	$74.78	$74.80	$74.80
Purchase #5	$86.74	13.118%	$98.1186	$98.12	$98.10	$98.10
Purchase #6	$61.49	9.769%	$67.497	$67.50	$67.50	$67.50
Purchase #7	$7.25	8.801%	$7.8881	$7.89	$7.90	$7.90
7 purchase totals =	$623.40		$676.7638	$676.77	$676.80	$676.80