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	$131.43	4.157%	$136.8935	$136.89	$136.90	$136.90
Purchase #2	$161.45	7.871%	$174.1577	$174.16	$174.15	$174.20
Purchase #3	$222.95	4.640%	$233.2949	$233.29	$233.30	$233.30
Purchase #4	$74.56	4.627%	$78.0099	$78.01	$78.00	$78.00
Purchase #5	$103.60	3.527%	$107.254	$107.25	$107.25	$107.30
Purchase #6	$8.73	8.624%	$9.4829	$9.48	$9.50	$9.50
Purchase #7	$162.32	7.372%	$174.2862	$174.29	$174.30	$174.30
7 purchase totals =	$865.04		$913.3791	$913.37	$913.40	$913.50