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	$62.63	4.166%	$65.2392	$65.24	$65.25	$65.20
Purchase #2	$135.89	8.787%	$147.8307	$147.83	$147.85	$147.80
Purchase #3	$191.90	13.452%	$217.7144	$217.71	$217.70	$217.70
Purchase #4	$93.64	7.368%	$100.5394	$100.54	$100.55	$100.50
Purchase #5	$83.27	5.163%	$87.5692	$87.57	$87.55	$87.60
Purchase #6	$241.78	10.696%	$267.6408	$267.64	$267.65	$267.60
Purchase #7	$40.79	7.341%	$43.7844	$43.78	$43.80	$43.80
7 purchase totals =	$849.90		$930.3181	$930.31	$930.35	$930.20