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	$121.56	12.450%	$136.6942	$136.69	$136.70	$136.70
Purchase #2	$152.44	9.397%	$166.7648	$166.76	$166.75	$166.80
Purchase #3	$31.45	3.417%	$32.5246	$32.52	$32.50	$32.50
Purchase #4	$117.43	5.314%	$123.6702	$123.67	$123.65	$123.70
Purchase #5	$170.87	11.639%	$190.7576	$190.76	$190.75	$190.80
Purchase #6	$89.30	4.522%	$93.3381	$93.34	$93.35	$93.30
Purchase #7	$26.59	4.145%	$27.6922	$27.69	$27.70	$27.70
7 purchase totals =	$709.64		$771.4417	$771.43	$771.40	$771.50