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	$169.71	11.282%	$188.8567	$188.86	$188.85	$188.90
Purchase #2	$82.27	10.152%	$90.6221	$90.62	$90.60	$90.60
Purchase #3	$17.73	10.290%	$19.5544	$19.55	$19.55	$19.60
Purchase #4	$175.29	13.315%	$198.6299	$198.63	$198.65	$198.60
Purchase #5	$39.68	5.635%	$41.916	$41.92	$41.90	$41.90
Purchase #6	$155.58	8.463%	$168.7467	$168.75	$168.75	$168.70
Purchase #7	$242.46	11.807%	$271.0873	$271.09	$271.10	$271.10
7 purchase totals =	$882.72		$979.4131	$979.42	$979.40	$979.40