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	$123.91	12.142%	$138.9552	$138.96	$138.95	$139.00
Purchase #2	$180.67	9.629%	$198.0667	$198.07	$198.05	$198.10
Purchase #3	$188.70	6.401%	$200.7787	$200.78	$200.80	$200.80
Purchase #4	$99.58	6.292%	$105.8456	$105.85	$105.85	$105.80
Purchase #5	$213.52	11.575%	$238.2349	$238.23	$238.25	$238.20
Purchase #6	$44.53	7.162%	$47.7192	$47.72	$47.70	$47.70
Purchase #7	$150.53	3.538%	$155.8558	$155.86	$155.85	$155.90
7 purchase totals =	$1,001.44		$1,085.4561	$1,085.47	$1,085.45	$1,085.50