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	$117.76	8.663%	$127.9615	$127.96	$127.95	$128.00
Purchase #2	$137.83	13.587%	$156.557	$156.56	$156.55	$156.60
Purchase #3	$199.89	4.284%	$208.4533	$208.45	$208.45	$208.50
Purchase #4	$128.94	4.272%	$134.4483	$134.45	$134.45	$134.40
Purchase #5	$123.57	12.621%	$139.1658	$139.17	$139.15	$139.20
Purchase #6	$37.40	10.828%	$41.4497	$41.45	$41.45	$41.40
Purchase #7	$123.32	5.150%	$129.671	$129.67	$129.65	$129.70
7 purchase totals =	$868.71		$937.7066	$937.71	$937.65	$937.80