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	$15.67	10.183%	$17.2657	$17.27	$17.25	$17.30
Purchase #2	$37.70	12.258%	$42.3213	$42.32	$42.30	$42.30
Purchase #3	$37.54	8.229%	$40.6292	$40.63	$40.65	$40.60
Purchase #4	$133.49	12.789%	$150.562	$150.56	$150.55	$150.60
Purchase #5	$153.36	4.378%	$160.0741	$160.07	$160.05	$160.10
Purchase #6	$135.28	11.672%	$151.0699	$151.07	$151.05	$151.10
Purchase #7	$80.40	12.292%	$90.2828	$90.28	$90.30	$90.30
7 purchase totals =	$593.44		$652.2050	$652.20	$652.15	$652.30