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	$138.78	8.224%	$150.1933	$150.19	$150.20	$150.20
Purchase #2	$119.32	3.582%	$123.594	$123.59	$123.60	$123.60
Purchase #3	$118.39	13.606%	$134.4981	$134.50	$134.50	$134.50
Purchase #4	$161.70	12.461%	$181.8494	$181.85	$181.85	$181.80
Purchase #5	$111.34	3.145%	$114.8416	$114.84	$114.85	$114.80
Purchase #6	$238.90	13.217%	$270.4754	$270.48	$270.50	$270.50
Purchase #7	$184.33	4.614%	$192.835	$192.84	$192.85	$192.80
7 purchase totals =	$1,072.76		$1,168.2868	$1,168.29	$1,168.35	$1,168.20