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	$81.38	3.332%	$84.0916	$84.09	$84.10	$84.10
Purchase #2	$35.94	12.250%	$40.3427	$40.34	$40.35	$40.30
Purchase #3	$176.30	6.558%	$187.8618	$187.86	$187.85	$187.90
Purchase #4	$183.30	9.345%	$200.4294	$200.43	$200.45	$200.40
Purchase #5	$80.93	6.586%	$86.26	$86.26	$86.25	$86.30
Purchase #6	$133.83	6.684%	$142.7752	$142.78	$142.80	$142.80
Purchase #7	$179.57	5.402%	$189.2704	$189.27	$189.25	$189.30
7 purchase totals =	$871.25		$931.0311	$931.03	$931.05	$931.10