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	$29.83	5.496%	$31.4695	$31.47	$31.45	$31.50
Purchase #2	$218.76	3.251%	$225.8719	$225.87	$225.85	$225.90
Purchase #3	$225.44	10.637%	$249.4201	$249.42	$249.40	$249.40
Purchase #4	$17.84	3.169%	$18.4053	$18.41	$18.40	$18.40
Purchase #5	$223.50	5.380%	$235.5243	$235.52	$235.50	$235.50
Purchase #6	$203.72	9.656%	$223.3912	$223.39	$223.40	$223.40
Purchase #7	$200.74	13.317%	$227.4725	$227.47	$227.45	$227.50
7 purchase totals =	$1,119.83		$1,211.5548	$1,211.55	$1,211.45	$1,211.60