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	$150.70	13.686%	$171.3248	$171.32	$171.30	$171.30
Purchase #2	$36.59	7.628%	$39.3811	$39.38	$39.40	$39.40
Purchase #3	$16.33	13.663%	$18.5612	$18.56	$18.55	$18.60
Purchase #4	$58.35	11.650%	$65.1478	$65.15	$65.15	$65.10
Purchase #5	$64.38	3.107%	$66.3803	$66.38	$66.40	$66.40
Purchase #6	$15.75	5.721%	$16.6511	$16.65	$16.65	$16.70
Purchase #7	$139.72	12.713%	$157.4826	$157.48	$157.50	$157.50
7 purchase totals =	$481.82		$534.9289	$534.92	$534.95	$535.00