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	$13.59	12.719%	$15.3185	$15.32	$15.30	$15.30
Purchase #2	$29.93	3.502%	$30.9781	$30.98	$31.00	$31.00
Purchase #3	$63.56	5.199%	$66.8645	$66.86	$66.85	$66.90
Purchase #4	$39.90	5.866%	$42.2405	$42.24	$42.25	$42.20
Purchase #5	$168.44	13.584%	$191.3209	$191.32	$191.30	$191.30
Purchase #6	$185.98	6.600%	$198.2547	$198.25	$198.25	$198.30
Purchase #7	$183.35	8.505%	$198.9439	$198.94	$198.95	$198.90
7 purchase totals =	$684.75		$743.9211	$743.91	$743.90	$743.90