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	$103.93	5.174%	$109.3073	$109.31	$109.30	$109.30
Purchase #2	$118.83	12.313%	$133.4615	$133.46	$133.45	$133.50
Purchase #3	$166.87	13.533%	$189.4525	$189.45	$189.45	$189.50
Purchase #4	$18.48	11.144%	$20.5394	$20.54	$20.55	$20.50
Purchase #5	$70.68	6.534%	$75.2982	$75.30	$75.30	$75.30
Purchase #6	$83.49	10.645%	$92.3775	$92.38	$92.40	$92.40
Purchase #7	$41.33	10.209%	$45.5494	$45.55	$45.55	$45.50
7 purchase totals =	$603.61		$665.9858	$665.99	$666.00	$666.00