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	$134.85	6.584%	$143.7285	$143.73	$143.75	$143.70
Purchase #2	$44.34	8.404%	$48.0663	$48.07	$48.05	$48.10
Purchase #3	$61.29	5.466%	$64.6401	$64.64	$64.65	$64.60
Purchase #4	$113.89	8.159%	$123.1823	$123.18	$123.20	$123.20
Purchase #5	$29.39	10.149%	$32.3728	$32.37	$32.35	$32.40
Purchase #6	$240.41	9.739%	$263.8235	$263.82	$263.80	$263.80
Purchase #7	$101.26	12.684%	$114.1038	$114.10	$114.10	$114.10
7 purchase totals =	$725.43		$789.9173	$789.91	$789.90	$789.90