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	$235.31	6.460%	$250.511	$250.51	$250.50	$250.50
Purchase #2	$176.50	13.804%	$200.8641	$200.86	$200.85	$200.90
Purchase #3	$236.99	4.849%	$248.4816	$248.48	$248.50	$248.50
Purchase #4	$110.94	7.561%	$119.3282	$119.33	$119.35	$119.30
Purchase #5	$247.88	4.291%	$258.5165	$258.52	$258.50	$258.50
Purchase #6	$92.52	10.278%	$102.0292	$102.03	$102.05	$102.00
Purchase #7	$18.64	4.648%	$19.5064	$19.51	$19.50	$19.50
7 purchase totals =	$1,118.78		$1,199.2370	$1,199.24	$1,199.25	$1,199.20