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	$141.78	12.508%	$159.5138	$159.51	$159.50	$159.50
Purchase #2	$219.92	11.732%	$245.721	$245.72	$245.70	$245.70
Purchase #3	$132.89	4.693%	$139.1265	$139.13	$139.15	$139.10
Purchase #4	$104.87	4.752%	$109.8534	$109.85	$109.85	$109.90
Purchase #5	$65.27	8.639%	$70.9087	$70.91	$70.90	$70.90
Purchase #6	$23.27	7.708%	$25.0637	$25.06	$25.05	$25.10
Purchase #7	$37.80	10.209%	$41.659	$41.66	$41.65	$41.70
7 purchase totals =	$725.80		$791.8461	$791.84	$791.80	$791.90