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	$25.90	5.267%	$27.2642	$27.26	$27.25	$27.30
Purchase #2	$96.25	7.654%	$103.617	$103.62	$103.60	$103.60
Purchase #3	$144.56	8.345%	$156.6235	$156.62	$156.60	$156.60
Purchase #4	$63.79	12.146%	$71.5379	$71.54	$71.55	$71.50
Purchase #5	$161.48	4.188%	$168.2428	$168.24	$168.25	$168.20
Purchase #6	$16.30	6.403%	$17.3437	$17.34	$17.35	$17.30
Purchase #7	$29.82	12.394%	$33.5159	$33.52	$33.50	$33.50
7 purchase totals =	$538.10		$578.1450	$578.14	$578.10	$578.00