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	$56.34	6.335%	$59.9091	$59.91	$59.90	$59.90
Purchase #2	$59.87	10.394%	$66.0929	$66.09	$66.10	$66.10
Purchase #3	$36.39	13.557%	$41.3234	$41.32	$41.30	$41.30
Purchase #4	$58.60	13.689%	$66.6218	$66.62	$66.60	$66.60
Purchase #5	$218.73	12.157%	$245.321	$245.32	$245.30	$245.30
Purchase #6	$33.44	8.495%	$36.2807	$36.28	$36.30	$36.30
Purchase #7	$66.54	8.777%	$72.3802	$72.38	$72.40	$72.40
7 purchase totals =	$529.91		$587.9291	$587.92	$587.90	$587.90