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	$144.48	9.601%	$158.3515	$158.35	$158.35	$158.40
Purchase #2	$50.44	12.593%	$56.7919	$56.79	$56.80	$56.80
Purchase #3	$89.85	13.776%	$102.2277	$102.23	$102.25	$102.20
Purchase #4	$90.67	11.687%	$101.2666	$101.27	$101.25	$101.30
Purchase #5	$26.32	12.197%	$29.5303	$29.53	$29.55	$29.50
Purchase #6	$111.60	10.488%	$123.3046	$123.30	$123.30	$123.30
Purchase #7	$81.61	6.463%	$86.8845	$86.88	$86.90	$86.90
7 purchase totals =	$594.97		$658.3571	$658.35	$658.40	$658.40