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	$56.78	7.801%	$61.2094	$61.21	$61.20	$61.20
Purchase #2	$52.25	6.387%	$55.5872	$55.59	$55.60	$55.60
Purchase #3	$152.31	12.527%	$171.3899	$171.39	$171.40	$171.40
Purchase #4	$245.34	3.313%	$253.4681	$253.47	$253.45	$253.50
Purchase #5	$60.41	11.313%	$67.2442	$67.24	$67.25	$67.20
Purchase #6	$248.72	9.646%	$272.7115	$272.71	$272.70	$272.70
Purchase #7	$78.41	4.440%	$81.8914	$81.89	$81.90	$81.90
7 purchase totals =	$894.22		$963.5017	$963.50	$963.50	$963.50