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	$30.34	3.605%	$31.4338	$31.43	$31.45	$31.40
Purchase #2	$81.72	10.783%	$90.5319	$90.53	$90.55	$90.50
Purchase #3	$159.34	10.795%	$176.5408	$176.54	$176.55	$176.50
Purchase #4	$157.63	7.102%	$168.8249	$168.82	$168.80	$168.80
Purchase #5	$165.39	3.161%	$170.618	$170.62	$170.60	$170.60
Purchase #6	$56.60	5.398%	$59.6553	$59.66	$59.65	$59.70
Purchase #7	$228.97	10.817%	$253.7377	$253.74	$253.75	$253.70
7 purchase totals =	$879.99		$951.3424	$951.34	$951.35	$951.20