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	$78.34	9.209%	$85.5543	$85.55	$85.55	$85.60
Purchase #2	$30.96	5.112%	$32.5427	$32.54	$32.55	$32.50
Purchase #3	$237.64	9.620%	$260.501	$260.50	$260.50	$260.50
Purchase #4	$39.47	8.577%	$42.8553	$42.86	$42.85	$42.90
Purchase #5	$30.66	13.544%	$34.8126	$34.81	$34.80	$34.80
Purchase #6	$76.68	7.362%	$82.3252	$82.33	$82.35	$82.30
Purchase #7	$141.45	3.183%	$145.9524	$145.95	$145.95	$146.00
7 purchase totals =	$635.20		$684.5435	$684.54	$684.55	$684.60