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	$139.40	6.388%	$148.3049	$148.30	$148.30	$148.30
Purchase #2	$67.54	12.304%	$75.8501	$75.85	$75.85	$75.90
Purchase #3	$83.39	7.444%	$89.5976	$89.60	$89.60	$89.60
Purchase #4	$10.57	13.209%	$11.9662	$11.97	$11.95	$12.00
Purchase #5	$240.86	7.260%	$258.3464	$258.35	$258.35	$258.30
Purchase #6	$63.90	4.141%	$66.5461	$66.55	$66.55	$66.50
Purchase #7	$32.29	12.561%	$36.3459	$36.35	$36.35	$36.30
7 purchase totals =	$637.95		$686.9572	$686.97	$686.95	$686.90