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	$17.47	6.619%	$18.6263	$18.63	$18.65	$18.60
Purchase #2	$65.34	10.764%	$72.3732	$72.37	$72.35	$72.40
Purchase #3	$8.80	6.652%	$9.3854	$9.39	$9.40	$9.40
Purchase #4	$108.76	3.581%	$112.6547	$112.65	$112.65	$112.70
Purchase #5	$41.38	3.434%	$42.801	$42.80	$42.80	$42.80
Purchase #6	$117.83	9.104%	$128.5572	$128.56	$128.55	$128.60
Purchase #7	$128.71	9.122%	$140.4509	$140.45	$140.45	$140.50
7 purchase totals =	$488.29		$524.8487	$524.85	$524.85	$525.00