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	$186.77	10.279%	$205.9681	$205.97	$205.95	$206.00
Purchase #2	$222.33	11.770%	$248.4982	$248.50	$248.50	$248.50
Purchase #3	$67.30	7.156%	$72.116	$72.12	$72.10	$72.10
Purchase #4	$152.78	4.461%	$159.5955	$159.60	$159.60	$159.60
Purchase #5	$154.71	6.180%	$164.2711	$164.27	$164.25	$164.30
Purchase #6	$25.26	5.844%	$26.7362	$26.74	$26.75	$26.70
Purchase #7	$78.59	13.660%	$89.3254	$89.33	$89.35	$89.30
7 purchase totals =	$887.74		$966.5105	$966.53	$966.50	$966.50