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	$80.33	5.250%	$84.5473	$84.55	$84.55	$84.50
Purchase #2	$61.68	11.639%	$68.8589	$68.86	$68.85	$68.90
Purchase #3	$18.38	10.659%	$20.3391	$20.34	$20.35	$20.30
Purchase #4	$90.76	4.180%	$94.5538	$94.55	$94.55	$94.60
Purchase #5	$92.82	8.283%	$100.5083	$100.51	$100.50	$100.50
Purchase #6	$100.58	4.839%	$105.4471	$105.45	$105.45	$105.40
Purchase #7	$106.43	9.801%	$116.8612	$116.86	$116.85	$116.90
7 purchase totals =	$550.98		$591.1157	$591.12	$591.10	$591.10