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	$28.89	9.358%	$31.5935	$31.59	$31.60	$31.60
Purchase #2	$35.44	5.476%	$37.3807	$37.38	$37.40	$37.40
Purchase #3	$227.55	9.539%	$249.256	$249.26	$249.25	$249.30
Purchase #4	$71.45	8.280%	$77.3661	$77.37	$77.35	$77.40
Purchase #5	$85.64	4.109%	$89.1589	$89.16	$89.15	$89.20
Purchase #6	$178.77	6.534%	$190.4508	$190.45	$190.45	$190.50
Purchase #7	$78.95	13.309%	$89.4575	$89.46	$89.45	$89.50
7 purchase totals =	$706.69		$764.6635	$764.67	$764.65	$764.90