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	$83.66	6.472%	$89.0745	$89.07	$89.05	$89.10
Purchase #2	$241.74	10.649%	$267.4829	$267.48	$267.50	$267.50
Purchase #3	$144.57	12.780%	$163.046	$163.05	$163.05	$163.00
Purchase #4	$152.73	5.338%	$160.8827	$160.88	$160.90	$160.90
Purchase #5	$76.26	11.826%	$85.2785	$85.28	$85.30	$85.30
Purchase #6	$147.58	4.390%	$154.0588	$154.06	$154.05	$154.10
Purchase #7	$163.84	10.234%	$180.6074	$180.61	$180.60	$180.60
7 purchase totals =	$1,010.38		$1,100.4308	$1,100.43	$1,100.45	$1,100.50