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	$51.66	8.252%	$55.923	$55.92	$55.90	$55.90
Purchase #2	$227.85	3.773%	$236.4468	$236.45	$236.45	$236.40
Purchase #3	$190.40	8.607%	$206.7877	$206.79	$206.80	$206.80
Purchase #4	$198.58	10.696%	$219.8201	$219.82	$219.80	$219.80
Purchase #5	$37.71	11.559%	$42.0689	$42.07	$42.05	$42.10
Purchase #6	$72.40	13.388%	$82.0929	$82.09	$82.10	$82.10
Purchase #7	$229.64	4.434%	$239.8222	$239.82	$239.80	$239.80
7 purchase totals =	$1,008.24		$1,082.9616	$1,082.96	$1,082.90	$1,082.90