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	$75.99	12.853%	$85.757	$85.76	$85.75	$85.80
Purchase #2	$209.99	10.435%	$231.9025	$231.90	$231.90	$231.90
Purchase #3	$158.29	9.188%	$172.8337	$172.83	$172.85	$172.80
Purchase #4	$82.63	3.508%	$85.5287	$85.53	$85.55	$85.50
Purchase #5	$124.75	9.710%	$136.8632	$136.86	$136.85	$136.90
Purchase #6	$204.29	5.632%	$215.7956	$215.80	$215.80	$215.80
Purchase #7	$49.59	13.530%	$56.2995	$56.30	$56.30	$56.30
7 purchase totals =	$905.53		$984.9802	$984.98	$985.00	$985.00