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	$96.82	3.822%	$100.5205	$100.52	$100.50	$100.50
Purchase #2	$102.47	8.675%	$111.3593	$111.36	$111.35	$111.40
Purchase #3	$208.37	9.118%	$227.3692	$227.37	$227.35	$227.40
Purchase #4	$193.48	10.471%	$213.7393	$213.74	$213.75	$213.70
Purchase #5	$177.96	6.481%	$189.4936	$189.49	$189.50	$189.50
Purchase #6	$162.52	3.149%	$167.6378	$167.64	$167.65	$167.60
Purchase #7	$190.27	4.638%	$199.0947	$199.09	$199.10	$199.10
7 purchase totals =	$1,131.89		$1,209.2144	$1,209.21	$1,209.20	$1,209.20