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	$77.41	12.272%	$86.9098	$86.91	$86.90	$86.90
Purchase #2	$91.32	9.781%	$100.252	$100.25	$100.25	$100.30
Purchase #3	$73.95	6.120%	$78.4757	$78.48	$78.50	$78.50
Purchase #4	$248.39	3.346%	$256.7011	$256.70	$256.70	$256.70
Purchase #5	$109.66	9.140%	$119.6829	$119.68	$119.70	$119.70
Purchase #6	$241.65	5.702%	$255.4289	$255.43	$255.45	$255.40
Purchase #7	$137.26	4.109%	$142.9	$142.90	$142.90	$142.90
7 purchase totals =	$979.64		$1,040.3504	$1,040.35	$1,040.40	$1,040.40