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	$82.50	8.266%	$89.3195	$89.32	$89.30	$89.30
Purchase #2	$131.39	7.727%	$141.5425	$141.54	$141.55	$141.50
Purchase #3	$18.35	3.140%	$18.9262	$18.93	$18.95	$18.90
Purchase #4	$98.93	4.682%	$103.5619	$103.56	$103.55	$103.60
Purchase #5	$98.50	5.227%	$103.6486	$103.65	$103.65	$103.60
Purchase #6	$188.95	13.149%	$213.795	$213.80	$213.80	$213.80
Purchase #7	$114.45	7.472%	$123.0017	$123.00	$123.00	$123.00
7 purchase totals =	$733.07		$793.7954	$793.80	$793.80	$793.70