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	$17.83	4.651%	$18.6593	$18.66	$18.65	$18.70
Purchase #2	$88.89	12.374%	$99.8892	$99.89	$99.90	$99.90
Purchase #3	$99.48	5.639%	$105.0897	$105.09	$105.10	$105.10
Purchase #4	$51.62	7.657%	$55.5725	$55.57	$55.55	$55.60
Purchase #5	$213.86	6.406%	$227.5599	$227.56	$227.55	$227.60
Purchase #6	$167.94	9.719%	$184.2621	$184.26	$184.25	$184.30
Purchase #7	$42.64	6.357%	$45.3506	$45.35	$45.35	$45.40
7 purchase totals =	$682.26		$736.3833	$736.38	$736.35	$736.60