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	$70.76	13.725%	$80.4718	$80.47	$80.45	$80.50
Purchase #2	$227.78	11.723%	$254.4826	$254.48	$254.50	$254.50
Purchase #3	$97.47	8.675%	$105.9255	$105.93	$105.95	$105.90
Purchase #4	$82.86	7.328%	$88.932	$88.93	$88.95	$88.90
Purchase #5	$137.80	3.681%	$142.8724	$142.87	$142.85	$142.90
Purchase #6	$64.69	11.627%	$72.2115	$72.21	$72.20	$72.20
Purchase #7	$61.42	5.266%	$64.6544	$64.65	$64.65	$64.70
7 purchase totals =	$742.78		$809.5502	$809.54	$809.55	$809.60