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	$50.73	8.323%	$54.9523	$54.95	$54.95	$55.00
Purchase #2	$229.86	6.812%	$245.5181	$245.52	$245.50	$245.50
Purchase #3	$106.52	5.663%	$112.5522	$112.55	$112.55	$112.60
Purchase #4	$225.92	13.210%	$255.764	$255.76	$255.75	$255.80
Purchase #5	$61.93	5.737%	$65.4829	$65.48	$65.50	$65.50
Purchase #6	$158.27	7.284%	$169.7984	$169.80	$169.80	$169.80
Purchase #7	$72.93	8.146%	$78.8709	$78.87	$78.85	$78.90
7 purchase totals =	$906.16		$982.9388	$982.93	$982.90	$983.10