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	$213.34	10.301%	$235.3162	$235.32	$235.30	$235.30
Purchase #2	$150.32	13.758%	$171.001	$171.00	$171.00	$171.00
Purchase #3	$70.56	11.822%	$78.9016	$78.90	$78.90	$78.90
Purchase #4	$38.63	3.654%	$40.0415	$40.04	$40.05	$40.00
Purchase #5	$5.26	3.158%	$5.4261	$5.43	$5.45	$5.40
Purchase #6	$196.84	10.418%	$217.3468	$217.35	$217.35	$217.30
Purchase #7	$113.40	3.658%	$117.5482	$117.55	$117.55	$117.50
7 purchase totals =	$788.35		$865.5814	$865.59	$865.60	$865.40