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	$86.74	4.547%	$90.6841	$90.68	$90.70	$90.70
Purchase #2	$6.45	10.469%	$7.1253	$7.13	$7.15	$7.10
Purchase #3	$59.35	12.177%	$66.577	$66.58	$66.60	$66.60
Purchase #4	$6.44	13.765%	$7.3265	$7.33	$7.35	$7.30
Purchase #5	$131.83	6.134%	$139.9165	$139.92	$139.90	$139.90
Purchase #6	$51.90	13.559%	$58.9371	$58.94	$58.95	$58.90
Purchase #7	$93.90	10.612%	$103.8647	$103.86	$103.85	$103.90
7 purchase totals =	$436.61		$474.4312	$474.44	$474.50	$474.40