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	$209.45	4.457%	$218.7852	$218.79	$218.80	$218.80
Purchase #2	$203.60	9.273%	$222.4798	$222.48	$222.50	$222.50
Purchase #3	$230.72	4.834%	$241.873	$241.87	$241.85	$241.90
Purchase #4	$127.83	7.475%	$137.3853	$137.39	$137.40	$137.40
Purchase #5	$155.80	3.173%	$160.7435	$160.74	$160.75	$160.70
Purchase #6	$153.77	7.689%	$165.5934	$165.59	$165.60	$165.60
Purchase #7	$83.41	11.395%	$92.9146	$92.91	$92.90	$92.90
7 purchase totals =	$1,164.58		$1,239.7748	$1,239.77	$1,239.80	$1,239.80