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	$244.35	5.170%	$256.9829	$256.98	$257.00	$257.00
Purchase #2	$115.92	7.185%	$124.2489	$124.25	$124.25	$124.20
Purchase #3	$13.96	13.726%	$15.8761	$15.88	$15.90	$15.90
Purchase #4	$118.77	3.624%	$123.0742	$123.07	$123.05	$123.10
Purchase #5	$111.59	12.477%	$125.5131	$125.51	$125.50	$125.50
Purchase #6	$37.47	12.845%	$42.283	$42.28	$42.30	$42.30
Purchase #7	$25.46	12.228%	$28.5732	$28.57	$28.55	$28.60
7 purchase totals =	$667.52		$716.5514	$716.54	$716.55	$716.60