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	$36.58	8.247%	$39.5968	$39.60	$39.60	$39.60
Purchase #2	$94.98	4.639%	$99.3861	$99.39	$99.40	$99.40
Purchase #3	$46.59	10.599%	$51.5281	$51.53	$51.55	$51.50
Purchase #4	$226.79	4.695%	$237.4378	$237.44	$237.45	$237.40
Purchase #5	$191.92	12.497%	$215.9042	$215.90	$215.90	$215.90
Purchase #6	$26.91	13.431%	$30.5243	$30.52	$30.50	$30.50
Purchase #7	$32.29	3.787%	$33.5128	$33.51	$33.50	$33.50
7 purchase totals =	$656.06		$707.8901	$707.89	$707.90	$707.80