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	$94.82	10.499%	$104.7752	$104.78	$104.80	$104.80
Purchase #2	$172.44	9.462%	$188.7563	$188.76	$188.75	$188.80
Purchase #3	$136.39	3.738%	$141.4883	$141.49	$141.50	$141.50
Purchase #4	$105.94	7.169%	$113.5348	$113.53	$113.55	$113.50
Purchase #5	$190.38	13.329%	$215.7558	$215.76	$215.75	$215.80
Purchase #6	$106.58	8.587%	$115.732	$115.73	$115.75	$115.70
Purchase #7	$33.96	10.425%	$37.5003	$37.50	$37.50	$37.50
7 purchase totals =	$840.51		$917.5427	$917.55	$917.60	$917.60