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	$131.61	5.150%	$138.3879	$138.39	$138.40	$138.40
Purchase #2	$87.48	3.765%	$90.7736	$90.77	$90.75	$90.80
Purchase #3	$243.25	4.158%	$253.3643	$253.36	$253.35	$253.40
Purchase #4	$103.46	9.736%	$113.5329	$113.53	$113.55	$113.50
Purchase #5	$21.39	5.110%	$22.483	$22.48	$22.50	$22.50
Purchase #6	$95.58	13.474%	$108.4584	$108.46	$108.45	$108.50
Purchase #7	$104.39	9.487%	$114.2935	$114.29	$114.30	$114.30
7 purchase totals =	$787.16		$841.2936	$841.28	$841.30	$841.40