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	$121.57	9.134%	$132.6742	$132.67	$132.65	$132.70
Purchase #2	$155.52	10.307%	$171.5494	$171.55	$171.55	$171.50
Purchase #3	$139.93	8.446%	$151.7485	$151.75	$151.75	$151.70
Purchase #4	$81.72	6.172%	$86.7638	$86.76	$86.75	$86.80
Purchase #5	$171.68	4.557%	$179.5035	$179.50	$179.50	$179.50
Purchase #6	$65.42	3.706%	$67.8445	$67.84	$67.85	$67.80
Purchase #7	$90.49	12.329%	$101.6465	$101.65	$101.65	$101.60
7 purchase totals =	$826.33		$891.7304	$891.72	$891.70	$891.60