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	$136.33	11.424%	$151.9043	$151.90	$151.90	$151.90
Purchase #2	$73.43	10.754%	$81.3267	$81.33	$81.35	$81.30
Purchase #3	$37.52	13.121%	$42.443	$42.44	$42.45	$42.40
Purchase #4	$219.80	8.246%	$237.9247	$237.92	$237.90	$237.90
Purchase #5	$165.82	7.114%	$177.6164	$177.62	$177.60	$177.60
Purchase #6	$109.33	10.461%	$120.767	$120.77	$120.75	$120.80
Purchase #7	$116.35	13.108%	$131.6012	$131.60	$131.60	$131.60
7 purchase totals =	$858.58		$943.5833	$943.58	$943.55	$943.50