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	$198.43	3.608%	$205.5894	$205.59	$205.60	$205.60
Purchase #2	$155.39	9.473%	$170.1101	$170.11	$170.10	$170.10
Purchase #3	$37.82	12.357%	$42.4934	$42.49	$42.50	$42.50
Purchase #4	$17.61	6.667%	$18.7841	$18.78	$18.80	$18.80
Purchase #5	$223.53	3.336%	$230.987	$230.99	$231.00	$231.00
Purchase #6	$156.96	7.369%	$168.5264	$168.53	$168.55	$168.50
Purchase #7	$24.61	12.716%	$27.7394	$27.74	$27.75	$27.70
7 purchase totals =	$814.35		$864.2298	$864.23	$864.30	$864.20