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	$60.30	12.692%	$67.9533	$67.95	$67.95	$68.00
Purchase #2	$14.34	4.462%	$14.9799	$14.98	$15.00	$15.00
Purchase #3	$188.63	12.196%	$211.6353	$211.64	$211.65	$211.60
Purchase #4	$217.55	11.216%	$241.9504	$241.95	$241.95	$242.00
Purchase #5	$96.43	7.264%	$103.4347	$103.43	$103.45	$103.40
Purchase #6	$80.93	11.218%	$90.0087	$90.01	$90.00	$90.00
Purchase #7	$88.56	13.177%	$100.2296	$100.23	$100.25	$100.20
7 purchase totals =	$746.74		$830.1919	$830.19	$830.25	$830.20