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	$163.80	13.485%	$185.8884	$185.89	$185.90	$185.90
Purchase #2	$115.59	7.410%	$124.1552	$124.16	$124.15	$124.20
Purchase #3	$60.42	4.669%	$63.241	$63.24	$63.25	$63.20
Purchase #4	$128.25	5.590%	$135.4192	$135.42	$135.40	$135.40
Purchase #5	$174.78	12.342%	$196.3513	$196.35	$196.35	$196.40
Purchase #6	$180.41	10.249%	$198.9002	$198.90	$198.90	$198.90
Purchase #7	$75.90	12.805%	$85.619	$85.62	$85.60	$85.60
7 purchase totals =	$899.15		$989.5743	$989.58	$989.55	$989.60