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	$78.74	9.119%	$85.9203	$85.92	$85.90	$85.90
Purchase #2	$123.71	12.777%	$139.5164	$139.52	$139.50	$139.50
Purchase #3	$158.31	13.790%	$180.1409	$180.14	$180.15	$180.10
Purchase #4	$212.60	11.691%	$237.4551	$237.46	$237.45	$237.50
Purchase #5	$137.96	4.783%	$144.5586	$144.56	$144.55	$144.60
Purchase #6	$62.32	11.482%	$69.4756	$69.48	$69.50	$69.50
Purchase #7	$202.28	10.455%	$223.4284	$223.43	$223.45	$223.40
7 purchase totals =	$975.92		$1,080.4953	$1,080.51	$1,080.50	$1,080.50