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	$169.61	11.743%	$189.5273	$189.53	$189.55	$189.50
Purchase #2	$100.66	3.713%	$104.3975	$104.40	$104.40	$104.40
Purchase #3	$80.78	7.221%	$86.6131	$86.61	$86.60	$86.60
Purchase #4	$173.58	3.616%	$179.8567	$179.86	$179.85	$179.90
Purchase #5	$78.80	8.613%	$85.587	$85.59	$85.60	$85.60
Purchase #6	$45.65	13.249%	$51.6982	$51.70	$51.70	$51.70
Purchase #7	$163.53	11.795%	$182.8184	$182.82	$182.80	$182.80
7 purchase totals =	$812.61		$880.4982	$880.51	$880.50	$880.50