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	$146.29	6.167%	$155.3117	$155.31	$155.30	$155.30
Purchase #2	$12.53	5.718%	$13.2465	$13.25	$13.25	$13.20
Purchase #3	$204.28	5.574%	$215.6666	$215.67	$215.65	$215.70
Purchase #4	$42.41	5.794%	$44.8672	$44.87	$44.85	$44.90
Purchase #5	$72.30	9.143%	$78.9104	$78.91	$78.90	$78.90
Purchase #6	$37.77	7.187%	$40.4845	$40.48	$40.50	$40.50
Purchase #7	$108.89	3.650%	$112.8645	$112.86	$112.85	$112.90
7 purchase totals =	$624.47		$661.3514	$661.35	$661.30	$661.40