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	$250.53	3.614%	$259.5842	$259.58	$259.60	$259.60
Purchase #2	$95.95	3.538%	$99.3447	$99.34	$99.35	$99.30
Purchase #3	$18.45	7.707%	$19.8719	$19.87	$19.85	$19.90
Purchase #4	$71.60	9.659%	$78.5158	$78.52	$78.50	$78.50
Purchase #5	$202.54	13.458%	$229.7978	$229.80	$229.80	$229.80
Purchase #6	$165.88	13.639%	$188.5044	$188.50	$188.50	$188.50
Purchase #7	$99.47	9.478%	$108.8978	$108.90	$108.90	$108.90
7 purchase totals =	$904.42		$984.5166	$984.51	$984.50	$984.50