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	$109.69	9.736%	$120.3694	$120.37	$120.35	$120.40
Purchase #2	$199.50	6.498%	$212.4635	$212.46	$212.45	$212.50
Purchase #3	$109.43	12.383%	$122.9807	$122.98	$123.00	$123.00
Purchase #4	$19.45	5.842%	$20.5863	$20.59	$20.60	$20.60
Purchase #5	$143.91	13.603%	$163.4861	$163.49	$163.50	$163.50
Purchase #6	$133.62	10.872%	$148.1472	$148.15	$148.15	$148.10
Purchase #7	$69.26	13.128%	$78.3525	$78.35	$78.35	$78.40
7 purchase totals =	$784.86		$866.3857	$866.39	$866.40	$866.50