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	$86.80	3.526%	$89.8606	$89.86	$89.85	$89.90
Purchase #2	$39.88	9.254%	$43.5705	$43.57	$43.55	$43.60
Purchase #3	$250.72	11.123%	$278.6076	$278.61	$278.60	$278.60
Purchase #4	$21.65	3.767%	$22.4656	$22.47	$22.45	$22.50
Purchase #5	$112.97	3.648%	$117.0911	$117.09	$117.10	$117.10
Purchase #6	$165.65	10.167%	$182.4916	$182.49	$182.50	$182.50
Purchase #7	$164.87	5.820%	$174.4654	$174.47	$174.45	$174.50
7 purchase totals =	$842.54		$908.5524	$908.56	$908.50	$908.70