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	$47.97	9.502%	$52.5281	$52.53	$52.55	$52.50
Purchase #2	$187.94	11.694%	$209.9177	$209.92	$209.90	$209.90
Purchase #3	$126.89	3.244%	$131.0063	$131.01	$131.00	$131.00
Purchase #4	$22.78	10.416%	$25.1528	$25.15	$25.15	$25.20
Purchase #5	$22.96	4.224%	$23.9298	$23.93	$23.95	$23.90
Purchase #6	$68.46	5.600%	$72.2938	$72.29	$72.30	$72.30
Purchase #7	$121.98	4.834%	$127.8765	$127.88	$127.90	$127.90
7 purchase totals =	$598.98		$642.7050	$642.71	$642.75	$642.70