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	$161.30	11.536%	$179.9076	$179.91	$179.90	$179.90
Purchase #2	$179.32	11.855%	$200.5784	$200.58	$200.60	$200.60
Purchase #3	$31.38	12.410%	$35.2743	$35.27	$35.25	$35.30
Purchase #4	$193.68	8.614%	$210.3636	$210.36	$210.35	$210.40
Purchase #5	$106.72	12.265%	$119.8092	$119.81	$119.80	$119.80
Purchase #6	$185.41	11.462%	$206.6617	$206.66	$206.65	$206.70
Purchase #7	$123.49	8.514%	$134.0039	$134.00	$134.00	$134.00
7 purchase totals =	$981.30		$1,086.5987	$1,086.59	$1,086.55	$1,086.70