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	$241.67	3.655%	$250.503	$250.50	$250.50	$250.50
Purchase #2	$235.89	6.587%	$251.4281	$251.43	$251.45	$251.40
Purchase #3	$68.81	3.731%	$71.3773	$71.38	$71.40	$71.40
Purchase #4	$152.89	9.714%	$167.7417	$167.74	$167.75	$167.70
Purchase #5	$227.40	6.215%	$241.5329	$241.53	$241.55	$241.50
Purchase #6	$17.67	10.391%	$19.5061	$19.51	$19.50	$19.50
Purchase #7	$189.79	12.353%	$213.2348	$213.23	$213.25	$213.20
7 purchase totals =	$1,134.12		$1,215.3239	$1,215.32	$1,215.40	$1,215.20