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	$20.88	4.858%	$21.8944	$21.89	$21.90	$21.90
Purchase #2	$97.89	5.655%	$103.4257	$103.43	$103.45	$103.40
Purchase #3	$96.56	12.473%	$108.6039	$108.60	$108.60	$108.60
Purchase #4	$80.27	12.584%	$90.3712	$90.37	$90.35	$90.40
Purchase #5	$181.87	10.236%	$200.4862	$200.49	$200.50	$200.50
Purchase #6	$154.25	10.830%	$170.9553	$170.96	$170.95	$171.00
Purchase #7	$167.94	8.804%	$182.7254	$182.73	$182.75	$182.70
7 purchase totals =	$799.66		$878.4621	$878.47	$878.50	$878.50