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	$23.47	9.109%	$25.6079	$25.61	$25.60	$25.60
Purchase #2	$24.26	8.269%	$26.2661	$26.27	$26.25	$26.30
Purchase #3	$148.88	8.482%	$161.508	$161.51	$161.50	$161.50
Purchase #4	$38.73	9.207%	$42.2959	$42.30	$42.30	$42.30
Purchase #5	$206.88	7.467%	$222.3277	$222.33	$222.35	$222.30
Purchase #6	$55.56	10.859%	$61.5933	$61.59	$61.60	$61.60
Purchase #7	$94.31	5.597%	$99.5885	$99.59	$99.60	$99.60
7 purchase totals =	$592.09		$639.1874	$639.20	$639.20	$639.20