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	$28.53	11.874%	$31.9177	$31.92	$31.90	$31.90
Purchase #2	$16.52	13.779%	$18.7963	$18.80	$18.80	$18.80
Purchase #3	$17.46	5.853%	$18.4819	$18.48	$18.50	$18.50
Purchase #4	$41.28	3.140%	$42.5762	$42.58	$42.60	$42.60
Purchase #5	$5.46	4.747%	$5.7192	$5.72	$5.70	$5.70
Purchase #6	$150.30	4.387%	$156.8937	$156.89	$156.90	$156.90
Purchase #7	$219.90	6.743%	$234.7279	$234.73	$234.75	$234.70
7 purchase totals =	$479.45		$509.1129	$509.12	$509.15	$509.10