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	$88.89	8.812%	$96.723	$96.72	$96.70	$96.70
Purchase #2	$179.82	5.243%	$189.248	$189.25	$189.25	$189.20
Purchase #3	$19.55	8.802%	$21.2708	$21.27	$21.25	$21.30
Purchase #4	$199.91	5.866%	$211.6367	$211.64	$211.65	$211.60
Purchase #5	$237.92	8.705%	$258.6309	$258.63	$258.65	$258.60
Purchase #6	$35.54	11.220%	$39.5276	$39.53	$39.55	$39.50
Purchase #7	$65.54	10.284%	$72.2801	$72.28	$72.30	$72.30
7 purchase totals =	$827.17		$889.3171	$889.32	$889.35	$889.20