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	$250.79	3.109%	$258.5871	$258.59	$258.60	$258.60
Purchase #2	$200.73	3.512%	$207.7796	$207.78	$207.80	$207.80
Purchase #3	$59.72	12.131%	$66.9646	$66.96	$66.95	$67.00
Purchase #4	$185.57	10.266%	$204.6206	$204.62	$204.60	$204.60
Purchase #5	$218.76	4.429%	$228.4489	$228.45	$228.45	$228.40
Purchase #6	$107.78	11.179%	$119.8287	$119.83	$119.85	$119.80
Purchase #7	$94.92	9.831%	$104.2516	$104.25	$104.25	$104.30
7 purchase totals =	$1,118.27		$1,190.4811	$1,190.48	$1,190.50	$1,190.50