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	$41.39	3.192%	$42.7112	$42.71	$42.70	$42.70
Purchase #2	$241.94	3.750%	$251.0128	$251.01	$251.00	$251.00
Purchase #3	$58.42	11.400%	$65.0799	$65.08	$65.10	$65.10
Purchase #4	$150.87	11.309%	$167.9319	$167.93	$167.95	$167.90
Purchase #5	$131.30	8.553%	$142.5301	$142.53	$142.55	$142.50
Purchase #6	$188.69	11.801%	$210.9573	$210.96	$210.95	$211.00
Purchase #7	$151.86	4.354%	$158.472	$158.47	$158.45	$158.50
7 purchase totals =	$964.47		$1,038.6952	$1,038.69	$1,038.70	$1,038.70